Reptiles? birds? or sometimes even mammals?

The trunk allows for breathing while the elephant is swimming across the lake. Under the moonlight, the similarity with Nessie would be amazing. Everything fits no matter what part or how much of the body goes out of the water. Its motion and speed are compatible with what we would expect. The ear can even stand for a leg. A swan has a similar silhouette, but the neck would move way too fast and no confusion could be possible.

Of course, the title also refers to the Lake's name.