A spokesman for Kent Police said there was nothing to suggest that "foul play or anything sinister" had taken place atBrooklands Lake, Dartford.
In a statement, the force added that "no criminal offences have been disclosed".
An investigation will continue though, conducted by Dartford Borough Council and the Environment Agency (EA), amid fears of contamination.
Officers set up a cordon and warned locals to stay away after a dog walker reported that three of her animals had become ill and died yesterday.
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Parkvets Veterinary Hospital in Footscray, Sidcup, said it knew of 10 dogs that had been affected, including the three which had died, while the surviving animals were being kept under observation.
A spokesman for Dartford Borough Council, which owns the land at the site, said: "We are waiting for the results of water tests from the EA and also any toxicology reports we get back from the vets as to what the possible cause is."