How to solve a large number of dead fish in fish ponds in summer?

It's hard to say. We must find out the cause of the dead fish first.

You can dissect the dead fish to see if there are any lesions in the internal organs. If you are sick, treat the disease first and change the water at the same time.

Needless to say, you are a professional fish farmer, and you don't know how to deal with it.