This bird's plumage seems to match that in big Sibley for "Adult nonbreeding (Sep-Feb)" Clark's Grebe.

Clark's Grebe +:
-- The eye has white in front and in back, with a dark stalk down to the bill, and black above.
-- Whitish flanks.
-- (not visible in this photo) Distinctly narrower black line down back of neck, compared to nearby Western Grebes.

Western Grebe +:
-- It's bill doesn't look as bright as that Clark's illustration; looks more like Western Grebe's bill color.

The Sibley Guide to Birds, Second Edition. Page 62

What do you think? Maybe hybrid?

Viewed and photographed from my kayak near the west shore of Priest Rapids Lake, about a mile-and-a-half north of Priest Rapids Dam, May 27, 2015. It was hanging out near, but not with, groups of Western Grebes.