Here's an historical cryptid that is not well known, but worth remembering. The term "dragon-worm" has been applied to a strange water monster which was reported in Switzerland in 1468. It swam out of Lake Lucerne and into the River Reuss. Details of its size and speed could not be determined.
There are quite a number of accounts of water monsters in Continental Europe that do not seem to swim frequently into the cryptozoological radar.