Just a day earlier, I had been talking to one of the speakers from the Dragonfly Society of the Americas annual meeting, speculating on why insects with aquatic adults were so much less colorful than their terrestrial or aerial counterparts. Then, while on a stakeout for Giant Darner (Anax walsinghami), I saw what looked like a huge green seed or nut in the water. Turned out to be this dead diving beetle. My best guess is that it's an unusually bright Cybister fimbriolatus, but I'm open to alternative ideas....