Police have warned the public to stay away from a lake as three dogs died after swimming in it and drinking from it.
A dog walker said that three of her animals became ill and died after going into Brooklands Lake in Dartford. Vets are still working to save a fourth dog.
Kent Police are working with the Environment Agency and said that it was not clear whether the lake is contaminated or caused the deaths, and are warning people as a precaution.
A spokesman said: "It is believed they (the dogs) got into the lake and drank from it. They came out and started fitting.
"Shortly after that three of them died and vets are attempting to resuscitate the other one."
Parts of the lake, which is popular with dog walkers and hikers, have now been cordoned off.
Kent Police said in a statement: "The circumstances are currently under investigation, it is understood the dogs were all being walked together.
"Police are warning people as a precaution, as yet the cause of the animals' illness is not known and it has not been confirmed if they were contaminated by anything in the lake."
The RSPCA has advised pet owners to contact their vet immediately if they are concerned their pet may have been poisoned.