Health alerts issued for three popular lakes

By ANNE BESTON

Health warnings have been issued for three lakes in the Auckland region advising people not to swim, fish or go boating because of toxic algal blooms.

Auckland medical officer for public health, Dr David Sinclair, issued the warnings yesterday after tests by Auckland Regional Council scientist Grant Barnes showed blue-green algal blooms had reached dangerous levels at lakes Spectacle and Slipper near the east coast south of Mangawhai, and at Lake Kuwakatai at South Head at the entrance to Kaipara Harbour.

"The major impact of algal blooms is the potential for human health impacts," said Mr Barnes.

The lakes are used mostly by locals and none of the them supply drinking water for humans. At least one of them supplies water for stock.

Blue green algae, or cyanobacteria blooms, have struck New Zealand lakes regularly in recent years, including Lake Rotoiti which is also currently under a health warning.

Water sampling by Mr Barnes of the region's eight lakes last week revealed Lake Spectacle was 18 times over the recommended safe limit for cyanobacteria.

Lake Kuwakatai was six times the recommended limit and Lake Slipper was a massive 38 times over.

At 50 ha, Lake Spectacle is about half the size of Takapuna's Lake Pupuke while Kuwakatai is about 29ha and Lake Slipper 9ha.

Cyanobacteria levels have been exceeded in most of Auckland's lakes over the past year including Lake Tomorata, just south of Lake Spectacle, Lake Wainamu on Auckland's west coast at Bethell's Beach and Lake Pupuke. Lakes Spectacle and Kuwakatai breached health guidelines in every sample taken since January last year.

The algae make water undrinkable, uninhabitable for fish and unsafe for swimming or even boating.

Toxins from the blooms can harm the liver and nervous system, cause skin rashes, hay fever and asthma attacks although children, the elderly and people with damaged immune systems are more susceptible.

Scientists have only just begun to research the blooms, detectable through improved technology since the late 1980s.

While blue green algal blooms are naturally-occurring, scientists believe the problem is made worse by development around waterways.

Stock effluent, fertilisers and septic tanks help raise levels of nitrogen and phosphorus which accelerates water degradation.

Mr Barnes said while some of Auckland's lakes were in good condition considering their intensively urban environment, the aim was to improve water quality in all the region's lakes.