Terrapins are quite common in a lot of British waters now, I have a lodge within five minutes of my humble abode which contains some whackers, vicious bloody things, probably introduced from bored pet owners, they do survive very well in this country though. The St Helens canal had for many years all sorts of strange things, Chilids being the most prevelent, me old mate Ronnie Pendleton use to catch them frequently, he wrote about them in the old NASG mag Freeline, , there was also a few South American albino Catfish swimming about in there, I can remember reading about a match angler who caught one in a match, he unhooked it, put it on the bank at the side of him and the bloody thing sprouted legs and ran between his legs and hopped off down the canal bank, he chased after it, not wishing to lose an extra few grammes in the contest, and the dam thing did about 300 yards and dived back in the canal, thats apparently a true story? I've actually got three different species of sturgeon in one of my garden ponds, amazing fish, and I know for a fact at least one water in Britain which contains some. I've fish out in france but never caught one although a few of the lads have had them. The last one I have on record was caught in the Rriver Don late 1700's, its set up in Doncaster's Natural History Museum, its incredible when you think these things used to be present in British waters!
A bit sad though when you consider some scientists are trying to re-introduce wild boar and the European wolf back into an environment which no longer exists!