Black mat algae found in Esk River could be toxic

Black mat algae has been discovered in the Esk River. Photo / File.

An algae which could be toxic to both dogs and humans has been found in the Esk River.

The Hawke's Bay Regional Council water monitoring team recently discovered large quantities of the algae in the Esk River at Waipunga Bridge.

The black slime is resting on the gravel bed upstream and downstream of the bridge.

It's also been discovered at Esk Park - but in smaller quantities.

A Hawke's Bay Regional Council spokesperson recommended that members of the public - especially dog owners - avoided the area as the algae (Phormidium) could be toxic to dogs.

Phormidium occurs naturally in shallow rivers and looks like a blackish mat that forms on rocks.

As it is a form of Cyanobacteria - blue-green algae - it can produce toxins which can result in serious illness. Current scientific understanding isn't clear about the conditions under which the toxins are produced or how it affects dogs and humans.

It doesn't help that dogs are attracted to the musky smell of the algae and dog deaths have been associated with Phormidium poisoning.

Phormidium can also be found at the side of river in the form of detached dark mats which dry in the sun and can turn slightly grey in colour.

Black mat algae was also discovered in the Waipawa River earlier this year, with the Hawke's Bay District Health Board posting warning signs along the river to warn dog walkers and hikers.