do you have goldfish and koi? if so, carp are extremely hardy, and they will pull through. our neighbors have a koi pond, and a few years back a blue heron family started living near it. our neighborhood has a lot of natural ponds, so heron, 3 foot long turtles, muskrats, and gigantic water snakes are common to say the least. well, the heron ate all the fish and guarded the tank like it was a million dollar bill. if our neighbors somehow got a chance to get fish in, they were gone in a few days. they eventually had to call in the animal control (or whatever its called out here in fox river grove) and remove the family of heron to a different location. just remember ponds are tricky, and stuff like that will happen, but in the end, it will all be alright.