I returned to the river today and was able to get some more pictures, this time of a solitary bird teetering on top of the lilypads:
Let me know what you think of my ID. The turning point came when I got to step 11 in my methodology: the National Geographic Birder's Journal. Sometimes it takes getting a fresh perspective to be able to see the way. Then I returned to my Sibley Guide to see his description of the Spotted Sandpiper that's when I picked up on the yellow bill notation in Sibley's description. Aside from the spots on the body, that was one of the most distinguishable characteristics and somehow I had missed it on my first pass through the book.