Regularly saw kingfishers on the K and A in the middle of Reading, saw some large aquatic mammal too, and mink. Plenty fish too. Chubb the size of whales (or Wales?) in the Thames at Staines.
I wouldn't drink it (untreated), but I'd swim in it; I don't think the waterways, certainly the ones that I use regularly, are in too bad a condition!
Excellent news (we lived plumb in the centre of the Wallingford-Reading-Henley 'loop' - and I have swum across the river at Whitchurch and lived to tell the tale).
Here in France we've got lots of kingfishers of various types and colours, and bee-eaters but also loads of coypu too. They are not so good, quite the reverse. Mind you, we also have some impressively big buzzards and eagles, too - aren't those red kites flying around Ipsden (etc.) terrific !