The occurrence has forced the Water & Sewerage Company Inc. (WASCO), to shut off water to residents supplied by the facility at Micoud.
The agency has called for comprehensive investigations and testing of the raw water source for the cause or causes which may be killing the fish.
WASCO said in a statement that the Water Resource Management Agency and the Environmental Health branch of the Ministry of Health had been contacted.
When the first fish kill occurred around the middle of this month, the agency had warned the public against using poisonous substances to harvest fish and crayfish for sale.
It said the dangerous practice compromised the supply of water and the lives of people.
It also announced that it had conducted “elaborate” cleaning and flushing of the treatment plant, reinstatement of the fish monitoring pond and fish, and monitored the fish in the pond for several hours.
Additionally, it said continual testing of the raw water as well as the treated water was done in order to be fully satisfied that all the necessary indicators were met prior to resuming the distributing the water to consumers.