Ah..the wonderful aerial predators saw the swimmers below. Hunting season time? Automatic air sounding devices (used quite often by DFG and habitat conservation agencies) are utilized to scare away birds. You may want to check it out? The device can use either propane or any compressed air. You can actually fashion one out yourself.

Leo

* Knowledge and experience yield wisdom. Sharing wisdom expand the generations with crucial knowledge. Unshared wisdom is worth nothing more than rotting manure.