And all over your pool only? Something about your pool is attracting them, I know bees are always in need of water, maybe bump the chlorine level by a bit for a while, they may hunt down another pool nearby with a lower level then.
If you don't have a nest anywhere nearby, look at your trees and neighbouring trees, some nests are hard to spot when they are using the actual tree as a nest - you will see some spots on the tree covered in bees where they enter/exit the hive (hollow tree or branch).