We had a similar situation. We have a row of aborvitae trees on one side of the pool. Last year a few birds made nests in the trees. When the eggs hatched the entire family would fly from the trees to the roof, dropping their bombs. Our pool and deck were covered. We have removed the nests this year, and continue to do so when the birds rebuild them. I am hoping that sooner or later they will get the hint. My sense is the nests may be near your pool or property as well and I recommend the same action. I like birds, but if it is a choice between a clean pool or them, I know which one I am choosing.