The Environment Agency is investigating after scores of dead fish were discovered floating in Westham Pond.
The alarm was raised over the weekend by visitors who were also concerned at the thick green water in the pond in Mortain Road.
As well as dead fish, there are also dead water snakes.
Environmentalists say there is no fresh water flowing into the pond from neighbouring Springfield Close.
Westham Parish Council is responsible for the pond and is due to issue a statement later this week.
Westham Village Conservation Group is urging people to contact the parish council.
A group spokesperson said on its Facebook page, “Many local residents are understandably upset about the deteriorating ecological health of the pond and members of our group have made representations to Westham Parish Council urging action and pointing out to the council the advice of various ecological experts, but to no avail.
“The key to solving the pond problem is getting the council to take swift, decisive action, based on sound ecological advice in order to restore the pond to good health as quickly as possible.
“And perhaps the key to making the council act is local residents sending in letters of complaint to Westham Parish Council.
“If you send such a letter, please include in your letter an explicit request for your letter to be shared with all of the Westham parish councillors