If you can get something in there to agitate the surface of the water, something like
Anything that will agitate the water surface will help. Even a trolling motor with part of the blades out of the water running on the highest setting. Just make sure that enough of the motor is in the water to keep it cool.
It'll help a lot. If not, then the fish will keep dying until there is enough O2 in the water to support the fish that are left. If there's decomposing organic matter in the pond, then there's the possibility of all the fish going belly up.
Silver lining is that this will allow you to start with a clean slate. You could renovate the pond, making it deeper and not worry about killing any fish in the process.
