Splash_King
The Scrubbiest of Hunters
I presume you're referring to the plesiosaurs (which were neither really fish nor dinosaurs), in which case I don't know, but it's worth bearing in mind they lived in a time when the Earth was rather warmer than it is now, so if anything it might be too cold for them now.
Well, I was shakily referring to a prehistoric (for lack of a better word, please excuse my stupidity) fish, for an example, something along the lines of a Promissum.
http://fossil.wikia.com/wiki/Promissum
I highly doubt Plesiosaurs could be alive today. Just as we both mentioned, the climate's changed to be much colder.
Hm, that makes me wonder... Perhaps the Loch Ness Monster is based off of a Plesiosaur?