Those whacky census bureau guys:

A small lake southeast of Lake Stevens has two different names, Bevis and Butthead – almost identical to snickering characters in TV’s “Beavis and Butt-head” show.
“That means someone is playing a joke, I think,” said Ken Brown, a land surveyor with the state Department of Natural Resources.
Brown said the department calls it Bevis Lake. The U.S. Geological Survey uses that name on its topographic map.
But the U.S. Census Bureau calls it Butthead Lake in its records.