Rotorua's pristine lakes deteriorating

Three of Rotorua's more pristine lakes are showing signs of worsening water quality, a new environmental report shows.

The report, by Environment Bay of Plenty, has revealed that Lakes Okataina, Tarawera and Tikitapu (Blue Lake) are showing early signs of degradation, and Lakes Rotorua and Rotoiti have declined further in quality over the past three years.

Lakes Water Quality Society chairman Ian McLean said the report raised concerns that Lake Rotorua could turn into a swamp if not treated quickly enough.

Environment Bay of Plenty environmental investigations manager John McIntosh said such a scenario was unlikely "for at least another 1000 years or more".

But the report showed what was happening within the lakes in the region.

The report has included information recorded since 1990, but features strongly comparisons from the past three years.

Compiled by scientist Paul Scholes, it is mostly based on a measurement known as the trophic level index, which combines the test results of various factors which affect water quality, such as nitrogen, phosphorus and visibility.

Lake Rotorua, although statistically not recording a large change within the past decade, has dropped to a level known as the "supertrophic" stage over the past year.

Previously "eutrophic", where the water quality is regarded as poor, it has deteriorated further.

Mr McLean described supertrophic as "the second-lowest category on the way to becoming a swamp".

Lake Rotoiti, linked to Lake Rotorua through the Ohau Channel, has suffered definite degradation over the past three years, the report says.

But Mr McIntosh said within the past year there had been no noted decline in the water quality of Lake Rotoiti.

Lakes Tikitapu, Tarawera and Okataina had early warning signs of degradation but were still considered to be three of the best lakes in Rotorua. Lake Rotoma is the most pristine lake of all the lakes in the district.

The report says it is too early to tell if the results from Tikitapu, Tarawera and Okataina were simply part of the lakes' cycles or the start of a downward trend.

Mr McLean said the report gave encouragement to the regional council and the Rotorua District Council to maintain a sense of urgency for work on the lakes.

"It shows quite clearly the size of the problem and the strong central government support that will be needed."

LAKE WARNING

The first health warning of the summer season is in place at Lake Okaro, 25km south of Rotorua.

A cyanobacteria toxic bloom means people should restrict contact with the water because of the risk of reactions such as skin rashes or nausea.

- NZPA