Bay of Plenty Regional Council has issued a health warning for a lake south east of Rotorua because of a blue-green algal bloom.
The council has added a modified zeolite mineral to Lake Okaro to deal with the bloom by taking phosphorus from the water.
It says the product, Aqual P, was applied by helicopter at the weekend and it will be several days before it is known if it has been successful.
The council says people should avoid entering Lake Okaro if the water has a musty smell, appears murky with a blue or greenish tinge or if there is scum on the surface.
