The worst frog mortality so far reported

[Click to enlarge]

This idyllic looking dew pond in the Derbyshire Peak District has the dubious distinction of being the site of the single largest amphibian mortality reported to us so far in the Big Pond Thaw survey.

Sadly at least 150 frogs were found dead here.

Thanks to Roger for the information and the pictures – including the rather grisly image below.

[Click to enlarge]

The worst frog mortality reported to us in the Big Pond Thaw survey


55 Responses to “The worst frog mortality so far reported”

  1. HeatherBuckley Says:

    I was surprised when I went into the garden and saw two dead frogs under the ice: why would they be there in winter? I thought they hibernated underground? My pond is only small so I broke the ice and buried actually three frogs sadly. Would like to know the reason if possible.
    I live in Clacton-On Sea and it has been an extremely cold winter.

  2. HeatherBuckley Says:

    Why would the frogs hang around during such a drop in temperature?

  3. Jeremy Biggs Says:

    Hi Heather

    Would you be able to fill in a Big Pond Thaw form?


  4. carol brooke Says:

    lost all our frogs in garden pond, all dead, please can anyone tell us what has happened. Live in Broad Hinton North Wiltshire/

  5. Jeremy Biggs Says:

    Hi Carol

    Almost certainly, if your pond was ice and snow covered during the cold weather, the frogs ran out of oxygen (or possibly were killed by a build up of ‘toxic gases’ that occurs in de-oygenated water.

    We’re collecting information on the ponds where this happened (and also where it didn’t) to improve advice on managing ponds in cold weather.

    Ice cover doesn’t automatically lead to reductions in oxygen: in my ponds, which are shallow, very clean and have a lot of plants under the water, oxygen rises when the pond is iced over.


  6. Pat Johnston Says:

    So far I have had nine dead frogs in my pond which have been bloated and floating on the top. In spring I usually have up to 60 frogs in the pond and have not had this happen in all the years the pond has been there which is 21 years. I have also lost 5 large fish this year. It was only iced over for a couple of days as I keep a hole in the ice most of the time. So this must be happening all over the country. I am in Central Scotland.

    • Jeremy Biggs Says:

      Hi Pat

      Interesting that you made a hole and still lost fish and frogs.

      Would you be able to fill in a Big Pond Thaw form (on the Pond Conservation website)?

      We’re trying to find out more about the ponds where mortalities occurred so we can improve the advice about managing ponds for wildlife in winter.


  7. Jane Miller Says:

    People are suggesting to me that the frogs have died from a virus rather than iced-over ponds, and that this was happening last year too. Is there any truth in this?
    I have filled in the Big Pond Thaw survey.

  8. Angela Merryweather Says:

    I found two dead frogs (lovely little things) once the ice on my allotment pond had defrosted – it had probably been iced over for nearly three weeks. They were buried in my pet cemtery. Then on Friday I found a beautiful frog which looked as it was praying under the water. Of course, it was dead unfortunately; it was about 6″ from nose to toe. I thought that because the pond was 4ft deep at one end and there are plenty of oxygenating plants, they would be OK. I do hope that I will get more visitors setting up home in their place – I now have a small football on the pond so that any survivors or newcomers will be able to get oxygen if it should freeze over again.

    • Jeremy Biggs Says:

      Hi Angela

      Deep water’s no guarantee of keeping oxygen high, contrary to what most pond making advice says. So that might partly explain the losses.

      Oxygenating plants should help but the big problem this winter was probably snow cover which blocks out light completely, stopping photosynthesis, and the oxygen that produces.

      Probably the best place to break the ice for animals to get to the surface is at the edge – which is where I think most animals would intuitively head to find breathable air.

      The edge is the place that natutrally defrosts first, and I expect (though I’ve no real hard evidence) this would be something animals might ‘know’ – i.e. have evolved to look out for.


  9. bill rogers Says:

    I have had the same problem , over 20 medium to large frogs and three fish have died over the last three weeks.
    This year, because I watched the programme ‘Winter watch’ and they said it was ok to leave the pond frozen, I did and now it seems the pond life has suffered. Is this the reason or is there some type of virus going around.

    • Jeremy Biggs Says:

      Hi Bill

      Snow Watch was reporting advice we (Pond Conservation) gave based on a variety of new observations we’d made on what’s actually happening in icy ponds.

      The thing to remember is that, although there’s lots of apparently well-established advice about what to do with ponds in winter – from a wildlife perspective, until recently there’s been no serious investigation of what is actually going on.

      Probably the main problem this year was the snow blocking out light – thus stopping photosynthesis in the ponds, which would usually keep oxygen levels up.

      In my pond we find that oxygen levels _increase_ under the ice, until snow covers the pond.

      Many people have reported making holes in the ice and still having dead fish and amphibians, which backs up what we believe is going on.

      The sure way of keeping oxygen levels up is to do what fish keepers have long done – which is run the pump or a fountain to either add oxygen directly to the water, or keep the water stirred so that de-oxygenated water is constantly brought back into contact with the air.

      Longer term, shallower ponds with clear water and plenty of underwater plants, and not too much organic material in the bottom, will probably be a safer bet.

      If you had a few minutes spare you might like to fill in the Big Pond Thaw form on the Pond Conservation website – we’re trying to find out as much as we can about the ponds where mortailities occured.


  10. steve share Says:

    We live on the Staffordshire/Cheshire border and have a pond roughly 10ft by 12ft by about 2 ft deep. Our pond was iced up for between a week and a fortnight. So far we have had about 20 dead frogs (of which 2 were small, probably young, ones). We have a quantity of oxygenating plants in the pond.

    If you wish us to fill in a Big Pond Thaw form we would be pleased to do so.

  11. David Says:

    I also found 15 dead frogs in our small pond – I never knew there so many there and very sorry to lose them. Lothian region Scotland

  12. Pete j Watkinson Says:

    [Wickham, Hampshire, 8-Feb-2010] Have lost two frogs this week. Pond without ice for the last week or so (~18″ deep). Had seen them very bloated but seemingly content on pond floor and in different locations on different nights. A second one appears now to be on it’s back on the bottom so I guess it will float in due course. Did loose two fish (~8″) following the ice melting some two weeks ago but another 3 are resonably active in the water and cetainly not gasping on the surface.

    Smaller pond frogs (~10″ water) are active up to the surface on nights with positive temperature and no losses.

  13. Bob Says:

    This is probably completely daft but are we absolutely sure they can’t hibernate under water? I noticed fifteen in my pond (in Kinver, South Staffs) on Saturday. They were all the right way up and sitting on the bottom. They seemed a bit bloated and a little on the white side so I fished them out thinking they were dead. However, for fear of burying them alive I put them under a pile of leaves – just in case. I have photos if anyone is interested – may upload them later when I have more time.

    • Jeremy Biggs Says:

      Hi Bob – frogs are fine underwater as long as there’s a bit of oxygen around – in cold water they don’t need very much.

      But when oxygen drops to zero, frogs are a goner within 4-7 days.


  14. Bob Says:

    I checked the ones I took out a few days ago and they were definitely dead. I also fished another ten out of the pond today. All dead. That’s 25 frogs. There were about 8 small ones. The others were quite big.
    Here are some photos:


  15. Bob Says:

    By the way, all my fish are fine.

  16. Ann Humphreys Says:

    We have had our pond for over 20 years but this is the first year we have had frog mortalities. My daughter and I fished out at least 30 of them, all dead, bar 2 which we found alive. This is the first winter we have had no fish in the pond so did not think to leave an airhole, could this be the reason?
    There are plenty of oxygenating plants in the water. We live in North Shropshire.

    • Jeremy Biggs Says:

      Hi Anne

      I think the lack of an airhole probably won’t have made much, if any, difference.

      Whether there’s a hole in the ice or not won’t have much impact on the amount of xoygen in the water (if you’ve got time, have a browse back through the blog for my comments on this).

      The other possibility – that airholes let toxic gases out – also doesn’t seem all the plausible to me, though we don’t have any real information on this issue yet.

      I strongly suspect that the problem has generally been snow cover on ponds that were already relatively low in oxygen, and this simply leading to a few days with no oxygen at all – and frogs can only survive 4-7 days, as far as we know, with no oxygen.

      When snow covers the pond, oxygenators can’t help – in fact then they would potentially make things worse because they would go on using up oxygen without producing it.

      We’ll be summarising soon all the feedback from the Big Pond Thaw survey whcih casts a bit more light on all of this.


  17. Deborah Ruston Says:

    I have just discovered 11 dead frogs on the ground surrounding my small garden pond (North Worcestershire) with one dead one floating in the pond. Most had bloated bellies and black bodies.

    Frogs usually return to the pond around the 11th to 14th February most years, so it was a shock to see so many dead frogs. The pond has been frozen for quite long periods of time during January this year, but the same has happened in previous years, with no detrimental effects on the frogs.
    We also have newts in the pond but, so far ,I have not seen any returning to the pond or found any dead ones.

  18. Eve Anderton Says:

    The children made the grisley discovery of 5 dead frogs on 14th and have just found another 7 while removing ice containing duck weed. All the frogs have been a good size.

    One of today’s find had a large amount of cloudy jelly like substance coming out of it. Any ideas?

    I will be working on the theory of toxic gases build up and having a good look at sorting out organic matter build up.

    The pond is artificial and has a diameter of 2.1m and a depth of 0.8m. Looks like I’ll be putting this site on my favourites and looking at makjng our inherited pond more nature friendly.

    We spotted newts last year but no sign as yet.

    • Eve Anderton Says:

      Should have said we are in Somerset.

    • Jeremy Biggs Says:

      Hi Eve – not sure what the cloudy substance was – possibly a female with eggs before fertilisation?

      On the organic matter: my suspision is that ponds with a lot of organic matter may simply have very low oxygen levels – but we haven’t proved that yet. And we don’t have any info about the toxic gases – if any.

      So we’ve seen pond with lots of organic matter and measured low oxygen, but we haven’t yet gone on to remove the organic matter and see a measurable recovery in oxygen.


  19. Paula Says:

    Not seen any frogs as yet but did hear a big splash when clearing out leaves last week, we had less frogs last year then in previous years. On a brighter note saw several newts last evening by torchlight.
    Advice needed also please, on the best way to enlarge my pond without disturbing it – I thought to make two ponds with a bog area between the two? Any other ideas?

  20. CLIFF PARKER Says:

    Today I noticed that all the frog spawn that was in my natural pond had disappeared. I put the net into the pond to dip for evidence and pulled out six dead frogs, all were pink in colour and no sign of any of the frog spawn. I have dipped a jar into the water and the water is a pink colour also. The fish pond on the opposite side of the garden is crystal clear and full of spawn but this will not last due to the fish. SHOULD I COMPLETLY EMPTY THE NATURAL POND AND START AGAIN WITH FRESH WATER?
    A further 20 dead frogs have been removed this morning

    • Jeremy Biggs Says:

      Hi Cliff

      More questions than answers!

      First, is it possible the dead frogs died under the ice? Or are they recent mortalities?

      Second, does the frog pond have a lot of organic matter?

      I ask so as to get some indication as to whether the pink water is due to purple bacteria (which commonly is casued by large amounts of organic matter).

      If you have a lot of of organic matter in the frog pond it might be a good idea to remove it and start again.

      I’d try to make sure that you only refill the pond with rainwater.

  21. CLIFF PARKER Says:

    Hi Jeremy.
    The frogs did not appear until after the prolonged spell of bad weather (the pond was frozen over for 15 days thick enough for the cat to run across it chasing a squirrel). Within one day of the pond thawing complete there was a lot of activity and frog spawn around the edge. We then had one night when the pond froze again but it thawed in the course of the day.I have netted the bottom of the pond this afternoon and there are some dead leaves but it does not seem excessive. The pond is only one year old: it was constructed last spring to replace the small pond that was only 4ft long x 3ft wide and only 10 inches deep. The new pond is 10ft x 8ft and about 3ft in the middle. The fish pond which is on the other side of the path about 10ft away is in perfect condition and full of spawn, but this pond did have a net over it in the Autumn to prevent leave from the many trees around the garden from falling in. Both pond have a large area of duck weed covering them which I try unsuccessfully to remove on a weekly basis.
    Cliff Parker

  22. chris camps Says:

    have had my garden pond (a big old bath i sunk in the garden) 20 years. VERY succesfully had hundreds of frogs bred from it. this year all dead! Theres nothing in there now, not even water insects! nothing has been spilt in the pond. the water is as clear as ever. plants are doing fine. what on earth can be going on? creepy and upsetting.

  23. Jeremy Biggs Says:

    Hi Chris

    Do you think it was the cold weather?

    I expect you’ve seen all the posts and comments on this blog to do with winter amphibian mortalities.

    A few people also found dead smaller animals after the freeze too.

    And these deaths have almost certainly were due to the exceptionally cold weather, and probably the lack of oxygen it caused, although we haven’t yet ruled out accummulation of toxic gases.

    And with some people finding hundreds of dead frogs in their pond (the most I’ve had reported to me was 300), this has been very upsetting.

    But I don’t think there’s anything worse happening than the effects of the exceptionally cold weather – probably the longest cold spell in the last 20 years.

    I think the frogs will sooner or later come back if we go on providing them with good ponds and good land habitat.


  24. CLIFF PARKER Says:

    I put a post on the 25/02/10 reporting the dead frogs and the smelly pink water in my pond. I decided to empty the pond yesterday (Saturday). I purchased a pump to make the job easier and faster. On reaching the bottom of the pond I found more dead frogs but surprisingly a greater number of live ones. I netted these out and cleaned out all the debris at the bottom of the pond. I then washed out the pond with the hose pipe and then re-emptied before putting in the new water from my rain water butts this has only filled a quarter of the water needed to fill the pond as I was doing this the rescued frogs were jumping back into the pond even though they had been moved away to be near the fish pond. This morning I have noticed a large number of frogs are now in this pond even though I have had to put a plank of wood up the side in case they want to get out before the pond is full of rain water.

  25. MarDean Dastrup Says:

    Our pond was covered with ice and snow for months this year. It is about three feet deep and fairly large. I put a styrafoam floating ball in the center for a large air hole. Also we put the bubble maker on under the ice. When the snow dissappeared I saw a dead fish and a couple of dead frogs close to the surface. After the ice melted I could see the bottom and many dead frogs. Every day I scoop out about 4 or 5. Today I dredged the bottom of the pond with the net under the plants in the mud and leaves. I have found close to 50 dead frogs. No live ones. The rest of the fish are fine. I didn’t even know that I had that many.They never lay eggs. And my fish never lay eggs either. I have never had a baby fish in my pond in ten years.

  26. mike morrison Says:

    In Inverness my pond has really been covered with snow and or frozen since December with brief respite. There are no signs of frogs in the large or small pond at all nor in the wood ponds I visit every year.

    A friend saw the dead frogs in muir of ord and suggested the cold had got them being cold blooded

    This is late in my experience over the years for any frogs to appear in this area by up to 3 weeks and really I do not expect much till we have a temperature of 10 degrees for a reasonable period of time when frogs and bees etc come out of hibernation.

    The frogs are not stupid…would you if you could have a long lie ?


    I have not seen any dead frogs, but there again I havent seen any frogs at all this year and no frog spawn, which is unheard of. My pond is kept ice free at one end all winter by a little waterfall feature. Is frog spawn late this year, might it still apear ??

  28. Pat Says:

    I have today found 12 frogs dead in my “barrel” pond it’s really upsetting. I’ve emptied the whole thing and it’s covered in a horrible purple slime – is this from the decomposing frogs??

  29. Pat Says:

    BTW I’m in great totham Essex

  30. carol brooke Says:

    great news after all our dead frogs, we have frogs spawn, thought we had lost all of our frogs but obviously at least two have survived. Thanks for such an interesting blog.

  31. Jeremy Biggs Says:

    Hi Carol

    Glad you’re enjoying the blog – maybe you’d like to support our work by joining up to Pond Conservation!

    Best wishes


  32. Bob Says:

    As a follow up to my earlier posts, I pulled three more dead frogs out last weekend. So this now has nothing to do with the snow and ice.

  33. Chris Says:

    Our pond is ten years old and has never had a problem until this winter. At the height of the winter the pond was iced over and we found frogs and several gold fish dead and stuck in the ice on the surface. During the thaw more frogs and fish were found dead, floating on the surface. The water turned very green and very smelly and all vegetation seemed decayed. On emptying the water another dozen or so large, bloated frogs were found at the bottom, which was very sludgy.

    • Jeremy Biggs Says:

      Hi Chris – I think many people were in the same situation as you because we had the coldest winter for 30 years.

      The weather killed a lot of frogs – and smaller numbers of other amphibians. We don’t know what other effects it had – maybe it’ll be a good year for pond animals and plants, maybe a bad year.

      We’re publishing a report on the effects of the freeze in the next day or two which Pond Conservation supporters, readers of the blog and other pond lovers have helped put together.


  34. Chris Says:

    Whoops sorry, were in Worcestershire.

  35. steve share Says:

    Following my previous entry and a suggestion made in the blog, we hired a pump and almost completely emptied our pond. There were possibly 20 more dead frogs in the bottom of the pond BUT there were a number of live ones (doing what frogs do at this time of year) and also some newts. After cleaning out as much silt as we could we used the pump to empty our three water butts to fill the pond. It wasn’t a quarter full so we put some tap water in to bring the level up to about a third full. How long it will be before we can fill the pond fully heaven only knows – we may have to resort to more hosepipe use (o. k. we know it’s bad practice but what else can we do!) Our trouble now is that half the plants are out of the water.

    • Jeremy Biggs Says:

      Hi Steve

      It’s no comfort, but I think you’ve come up against the most important fact which becomes obvious as soon as you start thinking about water quality as the main pond management issue – where to get that water from if you can no longer rely on the tap.

      But knowing that doesn’t help fill your pond!

      The animals won’t mind low water levels for a while. If you can protect your plants somehow in the interim (water plants are pretty tough) there should still be plenty of time to refill with rainwater, unless we go in to an exceptionally dry spring.

      The other thing to do is to find neighbours with water butts they are not using and scrounge their water!

      I did this in Abingdon last year (twice) to refill the Blue Peter pond with clean water – and I had to take the water all the way to London!

      One word of cation – if you do borrow other people’s water check that they haven’t filled their water butts with tapwater.


  36. Barry Coleman Says:

    I have been finding an unusually high number of dead frogs in and around my pond. I live in Staffs.

    Spawning activity was high this year and the pond has not frozen since. My fish (rudd) also seem to be OK.

    This is a long established and natural pond about 20 years old and I’ve never noticed this before. There are often one or two dead ones in the autumn and winter but not in the spring.

    My first thoughts were of some sort of contagious disease but it seems that many think it is the cold weather. I’m sure that they have survived this kind of weather before.

    I a way I’m glad that it’s quite common this year and it’s not something that may have contaminated my pond, from the garden.

  37. Alison Says:

    I topped up my pond using the hose pipe and two days later i noticed that there were alot of dead tadpoles in the pond. The volume of water added would probably be about ten percent of the whole of the pond. I feel gutted that my actions may have caused this to happen. Any ideas as to what has gone wrong please?

  38. Liz Says:

    December 2010 / Jan 2011
    We made a breath hole in our garden pond which is just over 2 feet deep.
    We could see our our gold fish swimming around and thought everything would be fine. The following day, we discovered a frog trapped between the new layer of ice that had formed, and thought perhaps we made a mistake in doing that ?
    As the big freeze began to thaw, we found 1 fish and 25 adult frogs and two juvenile frogs all dead in the pond, some were frozen in the ice with their heads popping out.
    (all frogs were dead -white eyes and bloated)
    We also have a smaller pond which is still frozen over & can see 3 adult frogs frozen in the ice…..any ideas what may have caused such a large death rate?

  39. jan Says:

    have just fished out 5 dead frogs, last year we lost about 7.
    We have a small pond which was completely frozen over for days in December.

    I had tried to clear the snow off the surface and keep a ball floating on it, but clearly to no avail.

  40. Anne S Says:

    I found your blog through a search for frozen ponds and very informative it is, many thanks.
    My query relates to spawning toads – following a week of very mild weather the toads have gone into the ponds to spawn but with the weather turning cold the water is freezing over during the night. We break up the ice first thing in the morning but have not seen any more spawning activity. Are the toads able to survive trapped under the ice once they have come out of hibernation stage?

  41. Jeremy Biggs Says:

    Hi Anne

    Where are you writing from?


  42. Anne S Says:

    I’m a northern Scot, recently retired to the French Dordogne so the event of toads, and possibly frogs, spawning in January is a completely new experience – as are the large temperature variations. (20c last week, down to -10 last night)
    On the subject of new experiences – the sight of hundreds of what appeared to be “corks” bobbing to the surface of the water took us by surprise last summer. The corks turned out to be newts on the day they changed to surface breathing, do you think they will return to where the were spawned this year?

    On the topic of the thread all seems alive and well although we have had many weeks of ice cover on all the ponds. I did remove the snow at the edges where we could reach and broke the ice for the deer that come to drink.

  43. Jeremy Biggs Says:

    I don’t think toads will be very good at surviving for long underwater without oxygen – however, if ice is freezing and thawing I’d guess there might be enough oxygen around for a night, but that is a guess. Perhaps you could make a hole so they can get to the air (assuming they’re bright enough to find the hole)?


  44. heather Says:

    Has anyone ever considered Acid rain or snow, melting in spring would destroy pond life… pollution in the air precipitating…? In canada it kills fish eggs in some areas… wondering if there is a connection…

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