Yup – that’s it. People almost certainly added these water lilies – lilies naturally only spread by rhizomes or by floating on floodwater – they’re too heavy to spread any other way.

Maybe people do it because they don’t want to put spare lilies on the compost heap; maybe some think it’s the right think to do – after all ponds and water lilies are often seen as automatically going together.

Whatever the reason, it’s common to see lilies in ponds which are easy access: and in the New Forest lilies are not the worst problem by any means. Lilies at least don’t spread too much.

But hundreds of ponds in the Forest now have New Zealand Pygmyweed (Crassula helmsii) which came from garden centres and then spread by a variety of routes: dumping, accidental introduction to the countryside with other plants (this happened to us in the early 1990s), spread by wild animals and, particularly in the New Forest, by cattle and ponies.

You can see it with fish too: there’s a study of ponds in Epping Forest which shows ponds nearest roads and car parks have most non-native fish. The conclusion is clear.