Man I tell you this sort of things happens alot!! What ever became of the other guy who woke up one day and had these things in his pond..He SWARES that there was NO WAY that these things could have come from in flow...He says that He has a straight run off pond...This seems to be an on going debate. I really hope you find a way to get rid of them....
Some people seem to sware they come by way of "ol Big Bird Foot" :rolleyes: ...but I don't know
Be carfull and best of luck...