Toxins in Doctor's Pond, Great Dunmow have poisoned a large number of fish.
Fire crews counted 35 dead fish in the water on Saturday, September 11 after reports of a poisonous chemical in Doctor's Pond.
The chemical was discovered by Great Dunmow Town Council, with help from the Environment Agency, after a large number of fish died.
The Environment Agency found that blue-green algae had bloomed in the water, releasing a naturally-occurring toxin which can prove fatal to some wildlife.
Caroline Fuller, Great Dunmow Town Council clerk, said: "Late last week there were fish reported dead in the pond.
"We brought them out and discovered they died from a sort of chlorine poisoning.
"We called the Environment Agency. They concluded that as cold rainwater ran into the pond, warmer water rose up.
"This can cause blue-green algae to bloom, which releases toxins."
Caroline added: "We are confident that the fish population will recover."
Essex County Fire and Rescue Service helped aerate the pond, which can help improve water quality.
A fire service spokesperson said: "Over the weekend, on-call firefighters from Great Dunmow helped to save more than 30 fish in a local pond.
"The crew was called by the Environment Agency to aerate a pond in Star Lane, Great Dunmow at 12pm on Saturday after 35 fish had been killed in the water.
“Crews used main jets to aerate the pond and left the scene in the care of the Environment Agency."
The town council has temporarily suspended fishing at Doctor's Pond.
To improve water quality, equipment to oxygenate the pond is temporarily in place.
Caroline thanked anglers for their patience.
She added: "Thank you to the residents who reported the problem.
"Thank you also to everyone who got involved with the clean up effort over the weekend."
The Environment Agency says blue-green algae blooms naturally in the UK and can prove fatal to wildlife, farm animals and domestic pets if eaten.
Algal blooms should be reported to the Environment Agency on its 24-hour incident hotline: 0800 80 70 60.
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