We tried everything to stop the blue heron--fishing wire to trip it, netting over the pond, etc. but it eventually got all the fish. Upset and frustrated I filled it in
Blue Herons are protected by the Migratory Bird Treaty Act of 1918, so we couldn't harm it.
We never had many frogs. But there did not seem to be an issue with the fish. Our Dachshund used to love to swim in the pond, we could not keep her out!