Janet Tweedy writes
In article , K
writes

Pond owners often do this as a way of keeping algal growth down by
removing some of the nitrogen.

Can you do this in a pond with fish as well as wildlife Kay?

I think it depends on how you are growing the fish. I have green tench
in my pond, and of course there's no problem with growing watercress
(which is a UK native) in any pond with fish. But if you are keeping
your fish in a weed-free pond, then you probably won't want the
watercress in there.

--
Kay