They look like Gambusia to me. A livebearer native to North America

looks like a molly or platy to me

If they are tropicals that were recently released in a lake in your area (Oregon, from your profile?) I'd think the water would soon be too cold in the lake if not already so, and they wouldn't survive those cold water temperatures through the winter most likely? I can't tell you what fish they are for sure, but I think if it's a case of someone releasing an "exotic" species thinking they'd survive anywhere where there's fresh water, and they're not to bright.
On the other hand "exotic" fish in the wrong places here in the U.S. can pose serious problems for our native wildlife and aquatic life especially!! What's the name of those "exotic" fish that are really a worry to environmentalists since they've been found in several locations in U.S. lakes and evidently those can leave the water on occasion and move a fair distance over land to the next bit of water or even rivers?? I'd say walking catfish, but I'm not sure it's the same species?

Does the Dept of health in your area release mosquito fish every year? Sandy

it looks like a female guppy to me...i just started rasing them so im no expert....

the fish you were talking about that leaves the water from time to time is called the snake head and are banned from the US now not to say that arent here.

they are mosquito fish. A live bearer like mollies and platty's and great for a pond with koi keep mosquitos down and provide food for koi with their fry.