Warning over toxic algae in Waikanae River

File photo / Paul Estcourt

The Greater Wellington Regional Council is warning people using the lower Waikanae River following an increase of potentially toxic blue-green algae.

Weekly monitoring by staff from Kapiti Coast District Council has identified moderate growth of the algae in the river at Jim Cooke Park. Medium risk warning signs have been posted to alert river users.

Greater Wellington environmental monitoring and investigations manager Ted Taylor said a two-tiered warning sign system is used to advise river users of the risk from toxic algae.

"A medium risk sign means users can still swim or walk their dogs but should check first for any algal mats. A high risk sign means people should avoid contact recreation and dog walking in that part of the river," he said.

Blue-green algae are microscopic organisms that are naturally present in many New Zealand waters, including relatively "clean" waters. Algal growth increases when river flows are low and stable and temperatures consistently warm.

The toxins produced by blue-green algae can be fatal to dogs, which are particularly susceptible to exposure because they like to scavenge near water.

Contact with blue-green algae toxins may also cause vomiting, diarrhoea and skin irritations in humans.

- NZ Herald staff