A health warning has been issued over high levels of potentially toxic algae at Lake Wiritoa, near Marton, in Rangitikei.

MidCentral Health said today that tests carried out by Horizons Regional Council had shown very high levels of potentially toxic blue-green algae (cyanobacteria) in the lake.

Health warning signs will be placed at Lake Wiritoa and people were advised not to use the water for recreational purposes.

Cyanobacteria may produce toxins that are harmful to humans and animals if swallowed or through contact with skin, such as may occur when swimming, water skiing or kayaking.

Meanwhile, a warning previously issued for Dudding Lake has been lifted. Levels of potentially toxic blue-green algae previously reported have declined, but people should still avoid recreational contact with the water at Dudding Lake if it was cloudy, discoloured or has small globules suspended in it.

Exposure to cyanobacterial toxins may cause symptoms such as skin rashes, nausea, stomach upset and tingling and numbness around the mouth or finger tips.