Low levels of algae good for swimmers

Lower than expected levels of algae in Manawatu's rivers have meant good news for swimmers but disappointment for researchers.

None of the 35 sites visited by Horizons Regional Council's science team in the past week exceeded guidelines for blue-green algae, also known as cyanobacteria.

Horizons freshwater and science manager Jon Roygard said Horizons was studying factors that led to blue-green algae growth and what caused it sometimes to produce toxins.

"We actually had researchers from Niwa, Cawthron and the University of Canterbury scheduled to look at cyanobacteria mats over the weekend but with such low levels there's not enough for them to study.

"That's not to say it won't come back. As cyanobacteria grows rapidly under the right conditions, we have permanent signage up along the Mangatainoka River at SH2, the Tokomaru River at Horseshoe Bend and the Manawatu River at Hopelands," he said.

When blue-green algae blooms, it appears as a slimy black or dark brown mat on the rocks. Growths can dislodge and float downstream or dry out on gravel at the sides of rivers or streams as water levels drop.

Toxins produced by the algae can be harmful to people and animals. It is recommended that, as a precaution, people avoid using a river or stream should they observe musty-smelling, black, slimy, mat-like growths on river bed stones.

Horizons summer water quality monitoring programme runs until the end of April.

The weekly results can be viewed online at the swim spots section of horizons.govt.nz.

Manawatu Standard