Tens of thousands of the fish, mainly carp and tilapia, were found floating on the surface of the pond, dead from a lack of oxygen.
A Fishery Department official said the cause of death was probably hydrogen sulfide, which formed from a combination of bread that people threw into the pond to feed the fish, and fish feces.
The gas, plus the prolonged hot weather, finally deprived the fish of oxygen.
Phra Kru Sunthorn Kittiwat, the abbot of the temple, also known as Wat Nong Kram, said a backhoe was used to take out 2-3 tonnes of dead fish, and more oxygen was added to the water since many of the fish remained alive.
In the longer term, he was advised to clean up the pond and treat it with lime before the fish could be released back into it.