I mentioned seeing Water Forget-me-not (Myosotis scorpioides) a few days ago in the shallows of the River Hiz in Hertfordshire. Saw more today further upstream. Very similar in appearance to the Field Forget-me-not (Myosotis arvensis) and the Wood Forget-me-not (Myosotis sylvatica). Basically the same plant adapted to different habitats; distinctions between species can be marginal.

 For example I also noted seeing Marsh Woundwort (Stachys palustris) which looks a lot like Hedge Woundwort (Stachys sylvatica). They sometimes cross to create the naturally occurring hybrid Stachys x ambigua.