Algae alert in Masterton | Wairarapa News | Local News in Wairarapa

Toxins in Henley Lake have forced Masterton District Council to warn dog walkers not to let their animals off leads.

Parks and recreation services manager Grant Hathaway said the warning follows the discovery of toxins related to the decay of algae bloom.

"A health warning was issued earlier this week and signs have been put up at the lake after localised algae blooms were identified. This is a cautionary approach taken by council to ensure that lake users are not exposed to these toxins," he said.

"Exposure to cyanobacteria may cause symptoms such as skin rashes, nausea, tummy upset and tingling and numbness around the mouth or tips of fingers. If you or your pets experience health symptoms after contact with contaminated water, contact your doctor or vet immediately," Mr Hathaway said.

He described the toxin as causing "a thick surface scum" covering localised areas of the lake shoreline.

Also observed was a light blue/white streak of decaying cells that are releasing their pigments. This was a common occurrence during bloom decline.

"Cyanobacteria occur naturally but can increase rapidly during summer. If the water is cloudy, discoloured, or has small globules suspended in it, avoid all contact. Not all cyanobacterial blooms are visible to the naked eye and toxins can persist after the bloom has disappeared."

"Cyanobacterial concentrations can change quickly with changing environmental conditions such as wind. If a health warning is in place, avoid contact with the water."

Mr Hathaway said council would continue to monitor the lake during summer and the public would be advised of any changes in water quality that pose a threat to health.

A health warning was also issued at the Waipoua River, Masterton, at the start of the swimming season, as toxic blue-green algae growth increased.

Contact with the growth can cause vomiting, diarrhoea or skin irritations in people, and can be fatal for dogs.

Greater Wellington Regional Council senior environmental scientist Summer Greenfield said a visual assessment undertaken yesterday showed that fresh water that passed through the Waipoua River earlier in the week has removed virtually all potentially toxic algae.