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.
Ends
Additional information - Water quality results and actions
Water Quality Result 2012-2013InterventionsLake Rotorua
Target 4.2
Result 4.24Annual 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 3.95Measuring 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 3.5Lake 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 reticulationLake Okareka
Target 3.0
Result 3.15All trophic level index parameters improved.• Sewerage reticulation of lakeside communities
• Land-use change agreements
Tikitapu
Target 2.7
Result 2.75Water 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 reticulationLake 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 2.36Water 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 3.5Lake 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 2.94The lake still displays elevated annual phosphorus levels. The Trophic Level Index improved due to a decrease in annual
nitrogen.• Action plan in developmentLake Rotokakahi
Target 3.1
Result 3.69Water 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 5.42Water 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 3.93Water quality remains stable. • Rotomahana has not yet reached the trigger point to need an action plan.