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Friday, February 21, 2014

Low levels of algae a good sign for swimmers

Recent monitoring by Horizons Regional Council has found lower than anticipated blue-green algae levels in the Manawatu River catchment, making it a great time to enjoy the Region’s rivers.

None of the 35 sites visited by Horizons’ science team over the past week exceeded guidelines for the algae, also known as cyanobacteria. However, with more sunshine, warmer water and low flows on the cards, conditions could change over the next 10 days.

Horizons freshwater and science manager Dr Jon Roygard says Horizons is currently studying factors that lead to blue-green algae growth and what causes it to produce toxins in some cases.

“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 SH 2, the Tokomaru River at Horseshoe Bend and the Manawatu River at Hopelands,” he says.

When blue-green algae does bloom, 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.

While not all blooms are toxic, toxins produced by the algae can be harmful to people and animals. It is recommended that people avoid using a river or stream should they observe musty-smelling, black slimy mat-like growths on river bed stones as a precaution.

Horizons chief executive Michael McCartney says it’s great to see people getting out and enjoying all the Region has to offer but it is important to remain mindful of the risks.

“We have some wonderful swimming holes in our Region and we encourage people to get out and enjoy themselves this summer. At the same time, we need to be aware that rivers do change and it’s vital to look out for hazards such as blue-green algae, sunken logs, rocks and cliffs.”

People are advised to swim away from cliffs wherever possible and remember the following rules of thumb:

• If the water looks clean and clear and it is a sunny day, it should be safe to swim

• It is safest to wait three days after rain before swimming at river swimming spots

Horizons will continue its summer water quality monitoring programme until the end of April. The latest results are available online via the swim spots section of www.horizons.govt.nz

ENDS

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