"K" wrote
Janet Tweedy writes

Do you know the source of these streams? I have visions of people
chucking in watercress wherever they have running water and that may
not be advisable

Well, it is a British wild flower. They may get it anyway without
encouragement.

I'm sure I've read of water cress being grown in a garden soil bed -
presumably kept well watered. Or is that a different sort of cress?

--
Sue