A small ammonia leak from the Darigold plant at Issaquah spilled through a storm drain into the East Fork of Issaquah Creek and killed about 50 fish.

The Department of Ecology said the dead fish — some of which died naturally after spawning — included sculpin, trout and Chinook salmon.

The spill was discovered Wednesday by a state biologist who was surveying spawning salmon in the stream.

The dairy plant stopped the refrigerant leak by mid-afternoon. The total amount of the spill is unknown. The state Department of Ecology said Darigold is cooperating with the investigation into the cause of the spill.