I don't have a picture this time, unfortunately. But I do clearly remember what these weird things looked like.
I saw them twice: once, last July, in a mountain lake in North Carolina, and just a couple of hours ago in my neighborhood creek.
They're about 4-6 inches long, bottomfeeders, with four large triangular fins jutting out from the sides. They have a rather large head and a blunt, box-shaped snout. To put it from perspective, from above, they look like miniature nurse sharks.
But what intrigued me the most was the color: they were mainly a muddy black color, but they had two tannish-gray bars on their backs, and the snout and fins were rimmed with orange.
I've tried catching them, but they spook easily, and they usually spit out whatever I throw at them before I can set the hook. Here's a MS sketch of them:
I can't find any information online, because, honestly, how is one supposed to search for it if you don't even know the name.