At first I thought it might be a female rainbow darter, but now I'm not so sure. When I saw it in the wild, that was my first thought, that it wasn't a greenside. I was able to sneak up and get a quick photo before it spooked. The snout doesn't seem blunt enough and the markings are not consistent with a greenside, both found in this drainage (Potomac). But then again, the eyes don't match pictures of rainbow darter females that I see on the web (they are light, not dark). What do you think? Maybe the picture angle is giving me a false idea of what I'm looking at...
Regardless of the species, I like the picture