Tackle algal blooms immediately, says expert

By JO-MARIE BROWN

An Australian expert hired by the Ministry for the Environment to assess what is being done to help save Rotorua's sickest lakes says action should be taken immediately.

Dr Bruce Hamilton, a Perth consultant who specialises in environmental and natural resource management, was asked to evaluate the lakes last September after a report from the ministry's top official said toxic blue-green algal blooms could kill all life in Lake Rotoiti this summer.

The Herald revealed serious problems in several of the lakes in the area earlier that month.

Dr Hamilton visited Rotorua before Christmas and has made 37 recommendations on how to reduce the amount of nitrogen and phosphorus in Lakes Rotorua and Rotoiti which cause algal blooms to flourish in summer months and make the water unsafe for swimming.

High priorities include temporary groynes in Lake Rotorua to trap material carrying nutrients and diverting the Ohau Channel.

Oxygenation trials and the application of chemicals to absorb phosphorus are also recommended.

Most of the short-term solutions suggested are already being pursued by Environment Bay of Plenty and the Rotorua District Council, both of which are praised for their "excellent approach" to tackling the problem.

Action plans are now being formed by the two councils, local iwi, farming groups, residents and others affected to help individual lakes.

Work on Rotorua and Rotoiti's plan will officially begin at a public meeting on Monday.

The two lakes will be dealt with together because about 70 per cent of the nutrients which cause algal blooms to form in Lake Rotoiti flow into it from Lake Rotorua via the Ohau Channel.

Dr Hamilton's $40,000 report identifies more than a dozen measures which he says should be implemented to help restore water quality in the lakes.

The report also suggests an additional "wild card" option of using Roundup or other herbicides to control algal growth.

And as a cosmetic measure, oil pollution booms were suggested as a way of containing blooms and allowing them to be removed.

Dr Hamilton stressed that lakes were complex natural systems and it was vital to understand how all factors interacted with one other before permanent changes were made.

"There are many examples around the world where incomplete understanding has led to costly and environmentally damaging mistakes."

Environment Bay of Plenty chairman John Cronin said yesterday that it was pleasing that many of Dr Hamilton's recommendations were already being implemented.

The report was effectively a "seal of approval" and he hoped the Government would now contribute to the cost of restoring the lakes' health.

"It will cost us a lot of money to research some of the options recommended in this report and it will be even more costly when the time comes to carry them out."

Last month, Environment Minister Marian Hobbs announced that the Government would pay 45 per cent of the $81.5 million required to fix Lake Taupo's water quality problems, but no such offer has yet been made in respect of Rotorua's lakes.

Stopping algal bloom

To stop algal blooms from forming in Lakes Rotorua and Rotoiti, Australian expert Dr Bruce Hamilton says high priority should be given to:

* Improving Rotorua's system of stripping nutrients from its treated sewage.

* Constructing temporary groynes either side of the Ohau Channel.

* Designing temporary structures to divert the Ohau Channel down the Kaituna River.

* Continuing chemical trials to absorb phosphorus.

* Constructing or enhancing natural wetlands.

* Carrying out small-scale oxygenation trials.

* Continuing research on nutrient sources and lake processes.