When they say "in a lake", I'm pretty damn skeptical...surely someone would have found hard evidence of such a creature, besides the fact it would need a breeding population and food supply.
However, when they say "in the ocean", it gets me curious. Given the frankly weird shit that comes up from deep in the ocean, there could be literally anything down there. On my brother in laws trawler...which he used to remove the nets from and turn into a "normal" ship to take the family out for a week at sea fishing...we used to bait a line and with massive sinkers reel out a kilometer or more of line down into the deep off the edge of the continental shelf or on other deep areas of ocean, leave it for an hour or so, and see what we could pull up.
There used to be some odd looking stuff, I can tell you!
Of course, all this goes out the window if you're talking about Loch Ness...of
course Nessie is real!!

"One could spend their life looking for the perfect cherry blossom...and it would not be a wasted life"