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Positive water quality results for Rotorua Lakes

Positive water quality results for Rotorua Lakes
Immediate release: 2 September 2013

Rotorua Te Arawa Lakes Programme partners are pleased with recent results for water quality in several lakes.

Water quality in six lakes has improved in the past year, and water quality targets in several have been met or exceeded.

Work to improve water quality is done in partnership with Bay of Plenty Regional Council, Rotorua District Council and Te Arawa Lakes Trust. Annual monitoring outcomes have given some very positive results, Bay of Plenty Regional Council General Manager Natural Resource Operations Warwick Murray said.

Targets for each lake were set in consultation with the community, based on a point in time when people were happy with the water quality. The water quality measure, called the Trophic Level Index, is calculated based on four areas of lake health – total nitrogen, total phosphorous, water clarity and chlorophyll-a.
Mr Murray said the results were excellent, but the work was not yet done.

“To have six lakes with improved water quality from last year, and to have several lakes meet their water quality target, is a fantastic result,” Mr Murray said.

“These results would not have been possible without the support of the Crown and the Rotorua and wider Bay of Plenty community, and without the committed actions of the partners and funders of this programme.

“Lake Rotoiti’s water quality target was met for the first time and was the best since monitoring began in 1991. This shows the success of the Ohau Diversion Wall and sewerage reticulation. This is great news for the community and the programme,” Mr Murray said.

“Lake Rerewhakaaitu’s target was also met. Farmers in this catchment, with our support, are developing their own catchment plan to improve lake water quality and have committed to undertake all actions identified in the plan by 2015. They should be congratulated for the work they have already done and can take some heart from the improvements we are already seeing,” Mr Murray said.

While the annual results were promising, external factors such as climatic conditions could affect water quality from year to year, so it was important to look at the long-term trend in each lake.

The long-term trend in six lakes also showed improved water quality and while these results were encouraging, there was still a lot of work to be done on some lakes, Mr Murray said.

“Lake Rotorua and Rotoehu have improved significantly which is fantastic. The improvements have been primarily due to our in-lake interventions such as alum dosing and efforts by the Lake Rotorua farmers to improve farm management practices. Interventions like alum dosing have been very successful in improving water quality, but it is only buying time in the short term while we make the long-term changes needed to reduce nutrient losses in the catchment,” he said.

“Lake Rotorua water quality declined slightly from a Trophic Level Index of 4.08 last year to 4.24 this year. With the target of 4.2 this is still a good result, but we can’t be complacent and think we have fixed the lake. Significant reductions in the nitrogen load to the lake are required for sustainable improvements in the long-term.

“We are working with the Lake Rotorua Stakeholder Advisory Group (StAG) to develop rules that give farmers the certainty they need to make the necessary changes to meet the very challenging nitrogen reduction targets. A combination of short-term and long-term solutions are needed,” he said.

“Our focus has changed from short-term measures to long-term interventions, such as reducing nutrients from land-use activities. Over the next year a key priority for the programme is to progress the development of rules and an incentive scheme for Lake Rotorua, which will ensure the costs are fairly shared and that all stakeholders in the catchment do their bit to achieve the water quality targets for the lake,” Mr Murray said.


Additional information - Water quality results and actions

Water Quality Result 2012-2013Interventions
Lake Rotorua

Target 4.2
Result 4.24

Annual Trophic Level Index increased slightly from the previous year, but was still very close to target. Monitoring showed an increase in nitrogen and phosphorus levels.
While water quality is still the best it is has been for decades, for long-term sustainable water quality nutrient reductions from land-use are needed.
• Sewerage reticulation of lakeside communities
• Phosphorus Locking Plant
• Land-use change agreements
• Wastewater Treatment Plant upgrades
Lake Rotoehu

Target 3.9
Result 3.95

Measuring showed nitrogen and phosphorus levels were the lowest seen in 20 years.

Rotoehu was very close to meeting its water quality target

• Phosphorus Locking Plant
• Weed harvesting
• Land-use change agreements
Lake Rotoiti

Target 3.44
Result 3.5

Lake Rotoiti had the best water quality in decades and met its water quality target this year, for the first time since monitoring began in 1991.
• Ohau Diversion Wall
• Sewerage reticulation
Lake Okareka

Target 3.0
Result 3.15

All trophic level index parameters improved.• Sewerage reticulation of lakeside communities
• Land-use change agreements

Target 2.7
Result 2.75

Water quality in Tikitapu almost reached its TLI target and continued the trend of improvement from the last three years.

The annual average measurement of phosphorus has decreased in the last year and water clarity has improved by more than one metre.

• Sewerage reticulation
Lake Okataina

Target 2.6
Result 2.77

Water quality monitoring showed improvements in all TLI parameters with the annual nitrogen being lower than previously recorded.
• Action plan adopted in 2013.
Lake Rotoma

Target 2.3
Result 2.36

Water quality improved in the last year and small improvements occurred in all Tropic Level Index parameters.
• Main action of sewerage reticulation is on hold until the Waste Water Treatment Plant upgrade is resolved.
Lake Rerewhakaaitu

Target 3.6
Result 3.5

Lake Rerewhakaaitu was below its water quality target for 2013. Nitrogen levels in the lake have decreased over the last six years.
• Rerewhakaaitu farmers are developing their own catchment plan to improve lake water quality. The Primary focus is to prepare and implement a nutrient management plan for each farm.
Lake Tarawera

Target 2.6
Result 2.94

The lake still displays elevated annual phosphorus levels. The Trophic Level Index improved due to a decrease in annual nitrogen.• Action plan in development
Lake Rotokakahi

Target 3.1
Result 3.69

Water quality continues to show improvement since the severe algal blooms of 2009. Monitoring showed greatest improvement in nitrogen and chlorophyll-a levels with a slight decrease in phosphorus.• An Action Plan will be developed with lake owners.
Lake Okaro

Target 5.1
Result 5.42

Water quality has fluctuated over the last 10 years. A prolonged algal bloom and health warning has been in place since July 2012. • In-lake phosphorus treatment
• Constructed wetland
• Riparian management
Lake Rotomahana

Target 3.9
Result 3.93

Water quality remains stable. • Rotomahana has not yet reached the trigger point to need an action plan.

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