Toxic algae cause cattle deaths

A Waikato farmer has lost nine cattle after they drank from a lake so contaminated by toxic algae that levels were 760 times above animal drinking water standards.

The deaths have prompted public health warnings about algal blooms in several lakes in the region, and a university professor has described Waikato lakes as some of the worst in the country.

Farmer Des Friend found seven cattle and two calves dead on the edges of Lake Rotongaro, near Huntly, last Thursday after they drank the water.

Tests have shown algae toxin levels in the lake were 760 times above stock drinking water standards, while algae at the lake edge were 40 times above standards.
Most algae are harmless to humans and animals but the blue-green algae microcystis and the algae toxin microcystin are toxic, causing rashes, infections and gastric problems in humans.

Many Waikato lakes already have health warnings in place, because algal blooms are well above guidelines for swimming, boating or jetskiing.

The Environment Waikato programme manager for water, air and waste, Viv Smith, said the cattle deaths were unusual.

Parents had been warned to keep their children away from the lake as they risked skin infections and serious intestinal illness.

Dr Smith said algal blooms in Waikato lakes were a yearly occurrence as the weather got warmer.

David Hamilton, the Waikato University professor heading research into Rotorua's sick lakes, said lakes in the Waikato district were in a much worse state.

"Waikato's lakes are in really, really poor shape. They're almost a forgotten icon of the area."

He said nearly all of the lakes suffered severe algal blooms every summer, which caused them to be closed.

"They're in a severely degraded state."

Professor Hamilton said intensive farming was responsible for some of the problem, causing a build-up of nutrients from animal effluent, fertilisers and other run-off into the lakes over the years.

The nutrients fuelled algae growth, exotic fish species such as carp, catfish and rudd stirred up the lake bottom and winds also stirred the water. Together those factors meant the lakes were in an "awful" condition.

Algae are blooming at lakes Hakanoa, Kainui, Waahi, Whangape and Ngaroto, a popular boating spot.

Dr Smith said Environment Waikato had been working with farmers to mitigate nutrient run-off, but many of the lakes already had a historic build-up which could not be fixed.

"When the weather is warmer the blue greens [are] likely to proliferate."