Toxic algal bloom likely to spread

Okawa Bay, where the bloom is so bad that boating and fishing have been ruled out. Other areas are under threat as well. Picture / Alan Gibson

Toxic algal bloom plaguing Lake Rotoiti's Okawa Bay could spread to other Rotorua waterways if the weather stays calm, says Environment Bay of Plenty.

Environmental investigations manager John McIntosh said a health warning was issued for Okawa Bay on Friday, urging people not to use the bay for boating, drinking, bathing or swimming.

Monitoring results showed Lake Rotorua had a higher risk of breaking out into a lake-wide bloom.

If that were to occur, the algae would be pushed through the Ohau Channel, Okere Arm and eventually into the Kaituna River.

"That would be the worst-case scenario but if the weather remains calm then that will be what we see," Mr McIntosh said.

The risk of algal blooms would be high every year until remedial action on the lakes had been taken.

However, Lake Rotoiti was not likely to fall victim to a lake-wide bloom. Going by previous years Okawa Bay would be likely to remain in a bloom for at least a few weeks, if not longer.

"You can't predict the whole season," he said.

- NZPA