Warning toxic algal bloom may return to troubled lake

The buoy on Lake Tutira used to test water quality, leading to new warnings about potentially toxic algal bloom. Photo / Supplied

An explosion of algal bloom in Lake Tutira has resulted in the Hawke's Bay Regional Council issuing new warnings against entering the popular but troubled lake north of Napier.

The alert was issued by Hawke's Bay Regional Council yesterday, saying its environment science team has found evidence of high phycocyanin, indicating a "potentially toxic" blue-green algae cyanobacteria.

The Guthrie Smith outdoor education centre has been advised against taking school groups boating or kayaking on the lake, while council staff take further samples to confirm the algal bloom.

It's not the first time, with warnings issued in November 2008 and again in November 2012, leading to permanent placement of warning signs.

The Hawke's Bay District Health Board public health unit (now the Population Health Service) has in the past said exposure to the bloom can lead to varying health issues, including skin rashes and stomach upsets, hay fever and asthma attacks.

The Regional Council yesterday warned that with warmer temperatures and summer arriving, algal blooms can occur in streams, rivers and lakes around the region.

Algae are naturally found in waterways, but under favourable conditions they can grow to large numbers, causing them to "bloom".

Algal blooms in rivers occur more frequently when the flows are low in warm and dry weather. Algal blooms in lakes can also be stimulated by the input of additional nutrients following heavy rain.

In rivers, blooms may form mats. In the river these mats are often a shiny black colour, but when they wash up on river margins, they may be bleached pale by the sun. These dried mats can still be a risk.

In lakes, algal blooms may change the colour of lake water to red or bright green. Toxins may still be present in a lake after the colour from a bloom has returned to normal.

The council says dogs that scavenge along rivers are particularly susceptible to getting ill after contact with cyanobacteria.