After some research, I'm ready to go out on a limb and call this a Red Phalarope. Bill, head, and neck structure all looked thick to me in the field, and the light gray back and general plumage fit well with the photos I've been looking at. Interestingly, according to eBird, Reds are slightly more common than Red-necks in this part of the state in late October.
To clarify, I don't think there were Black-bellied Plovers at the lake. I found some promising lumps on the far shore with my binoculars in the rain, but when Chuck brought the scope careful scanning revealed only rocks and killdeer. Oh, and two snipe.
FOS Bufflehead, Lesser Scaup, and Am Tree Sparrow earlier this morning.
Chris Rurik
Denver CO