A lot of the Warblers I saw this year were juveniles, hatched this past spring and fully fledged by the end of summer, but not yet in their adult colours.
Juvenile Warblers are insanely difficult to identify. They’re all shades of grey, yellow, and olive green, and you have to get a really REALLY good look at them and then spend a lot of time with a field guide in order to figure out which one you just saw.
My parents had to cut down an old cedar tree that was threatening to fall on the dock (and the boats), and they left the brush in two piles in the water to create habitats for minnows and frogs. It worked beautifully, and in addition to the minnows and frogs, a number of young Warblers decided they liked them too. This little Black-Throated Green juvenile was one of them.