Water always attracted them up in Wyoming growing up. Even though we lived right on the N Platte, they would congregate by our well pits near the river. Little bastards were swarming and swimming in one of the pits one year when our pump went out. That wasn't a lot of fun getting them all out before I got in the pit to replace the pump! I think there were about 10 little ones in there, if I recall correctly. Aggressive little shits too!