Lake Waikopiro, next to Lake Tutira, has been confirmed as having dangerous levels of cyanobacteria.

Hawke's Bay Regional Council (HBRC) staff noticed people swimming at Lake Waikopiro this week and decided to take water samples. Results came back yesterday showing potentially toxic cyanobacteria was present above guideline safety levels, although below the levels of the larger Lake Tutira, which was reported in mid-January and remains unsafe.

HBRC has sent samples to the Cawthron Institute in Nelson, and is waiting on results of tests to assess if toxins have been released into the water or not.

The Hawke's Bay District Health Board has erected warning signage at Lake Waikopiro, and Medical Officer of Health Nicholas Jones says that people should avoid any contact with the water.

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"Toxic blooms can develop quickly, and skin contact can lead to skin rashes or eye irritation," Dr Jones said. "More serious effects can occur if toxins are consumed."

Dr Jones said people might not know cyanobacteria and toxin could be present even when the water appeared clear.