I have two that refuse to bathe properly, and one gets that too. The first time I saw it, I panicked. I caught him and rinsed his eyes with eye wash and worried myself crazy. Now I realize the problem is his personal hygiene habits. There is enough water to go around here, but he just doesn't bathe like he should. The other white muscovy drake is the same way. I periodically bring them in and put them in the bathtub the get cleaned up. They love it, but will not often get cleaned up the same way outside.
Oh great now I want to bring my big hunk of a bird into my house for a bath. Hubby might not be happy lol