Toxic algae has contaminated the lake in a popular Basildon beauty spot.
Basildon Council is warning visitors to Northlands Park, off Felmores, to avoid the lake as it has been confirmed that blue-green algae has been found in the water.
Dog owners should prevent their pets from swimming the toxic water.
Hugh Reynolds, Basildon Council’s parks and countryside manager, said: “We have put up warning signs near Northlands Park lake, however it’s important that dog walkers steer clear of the water and keep their animals on leads so they aren’t tempted to jump in.
“We expect the algae to naturally disperse in a week or two, but until then we’re advising visitors to be mindful and seek medical or veterinary advice if they are affected.”
Visit www.gov.uk/government/uploads for further advice.