I read a fair bit of US angling literature and beaver ponds are universally thought of as great, albeit temporary (years not months) features of any river system. Great fry refuges in the now rarer floods and a great place for fish to take up residence and grow far larger than in the river. Think what happened in Grafham, Rutland and Bewl etc when they were first flooded and the beavers do this for free every few years.
In my local river Colne some ponds were constructed to give some flood relief for fry, pre EE invasion, and the results were astonishing, surveys recorded fish density from a thousand fish a metre up in the river, including minnows, and the fishing was fantastic, quality chub, roach and dace and even some introduced Barbel did well.
Unfortunately the EEs ate a lot of the fish but have since deserted the river and there are no longer even any swims cut out. I really should get back down there in the winter. I'm sure the fish have made a comeback.