By Stacey Bodger
TAUPO - Concern is mounting that Lake Taupo is threatened by sewage from Turangi and effluent from boats.
The regional council, Environment Waikato, is demanding a $50,000 study before allowing Turangi permission to discharge waste water.
Environment Waikato will wait for the results of the study on the effects of Turangi's sewage on the lake and surrounding wetlands before deciding whether to renew resource consent.
And the Taupo harbourmaster and mayor and Department of Conservation officers are calling for new bylaws governing boats on the lake after people have been spotted dumping raw effluent.
Turangi's sewage is treated at oxidation ponds before the waste water is discharged on to irrigated land disposal fields and then to waterways which drain into wetlands near the lake.
The Institute of Geological and Nuclear Sciences will sample soil and water in the wetland, as well as the Hangarito Stream which flows into wetlands in the Tokaanu Basin.
Nutrient and metal levels will be measured and analysed to assess the impact of the oxidised effluent on the environment.
Environment Waikato lake specialist Dr Nick Edgar said a long-term series of fortnightly checks at a spot in the centre of the lake had shown nitrogen levels in the water had almost doubled in the past 20 years.
Nitrogen and other nutrients in the lake can increase weed growth, attract bird infestations and generally degrade water quality.
Dr Edgar said a number of factors could be responsible for the nitrogen increase, including waste water flowing into the lake, the increase in dry stock farming and forestry harvesting.
The purpose of such studies was to try to establish which single factor, or combination of many, was the cause.
Dr Edgar said there had been a steady decline in the quality of Lake Taupo's water over 20 years, but yearly monitoring of bacterial concentration at 18 sites around the lake showed it was well within safe levels for swimming and drinking.
Since Taupo changed to a land-based sewerage system two years ago, water quality in the Waikato River where the town's sewage used to be released had improved dramatically.
He said the dumping of effluent was illegal under the Resource Management Act and carried a maximum fine of $200,000.
Taupo harbourmaster Doug Brown said people on charter boats had reported two incidents of recreational boaties dumping effluent directly into the lake. The practice was despicable and threatened eventually to spoil the lake for others.
He said there were three pumping stations where boats could dispose of effluent.
By Stacey Bodger