Toxic algae warnings reissued
Fluctuations in toxic algae levels in Masterton’s Waipoua River have made it dangerous for swimmers and dogs in recent weeks.
In late December it was declared unsafe, though the latest reading on January 5 has seen the warning downgraded to ‘‘low risk’’.
Greater Wellington Regional Council environmental scientist Mark Heath said that, despite some recent rain, the water flow in the Waipoua was dropping and temperatures were rising, providing ideal conditions for algal growth.
The river has been deemed a hazard again thanks to an organism that was originally crucial to the oxygenation of the Earth.
‘‘The organism that causes the algae is a cyanobacteria and this family of bacteria has been around since the beginning of life on Earth.
‘‘There is confusion around the toxic algae, many people ask us if it is new or invasive. It is actually over 3 billion years old, but some things we are doing in terms of land use seem to be creating conditions it can thrive in.’’
Monitoring of the Waipoua River at Colombo Rd by the regional council shows that the amount of black or brown toxic algal mats growing on the river bed has reached dangerous levels.
Records show toxic algal blooms in the Waipoua have been a common occurrence over the past decade. This summer’s blooms are similar to what had been observed in previous years, Heath said.
The Waipoua has many characteristics which make it rather susceptible to toxic algal blooms including stable river flows, warm water temperature, high sunshine hours, and elevated nitrogen concentrations.
It is a slower flowing river that comes out of the hills and flows through a lot of agricultural land, as well as suburban and urban areas.
‘‘We will be undertaking a targeted investigation this summer to learn more about what is causing the toxic algal blooms in the Waipoua.’’
Ngati Kahungungu ki Wairarapa general manager PJ Devonshire said the iwi’s environmental staff were working with the council and other organisations to try to increase the health of Wairarapa rivers.
‘‘We will continue to fight for the health of our rivers. We do not want to get to a point where it is considered normal for people to not be able to swim.’’
If people are concerned about river safety they are advised to check theGWRC ‘‘Is it safe to swim?’’ webpage.
Waipoua River is showing fluctuating levels of toxic algae.