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Home > Latest News > Media Releases > Media Releases 2014 > October 2014 > Great News for Rotorua lakes water quality - Additional Information

Great News for Rotorua lakes water quality - Additional Information

Friday, 3 October 2014 10:00 a.m.

Water quality results

Of the 12 Rotorua lakes in the programme the long-term water quality trend shows:

  • Water quality is improving in Lakes Rotorua, Rotoiti, Rotoehu, Rerewhakaaitu, Rotomā and Tikitapu
  • Water quality is stable in Lakes Ōkataina, Ōkareka and Rotomahana
  • Water quality shows deterioration in Lakes Tarawera, and Rotokakahi
  • Water quality in Lake Ōkaro fluctuates and continued investigation is needed. 

About the programme

The programme of work to improve water quality is done in partnership with Bay of Plenty Regional Council, Rotorua District Council and Te Arawa Lakes Trust to meet targets set by the community.

How water quality is measured

The water quality measure is called the Trophic Level Index.  It is calculated based on four areas of lake health – total nitrogen, total phosphorous, water clarity and chlorophyll-a.

Lake by Lake Overview


Water quality summary


Lake Rotorua


Target 4.2

Result 4.2

Lake Rotorua is continuing to experience the best water quality in decades and is at its target for the third consecutive year. 

This has been achieved mainly due to alum dosing, but this is not a long term sustainable intervention.   

There is still a challenge to achieve nitrogen reductions in the catchment through rules and incentives.

  • Sewerage reticulation of lakeside communities
  • Phosphorus Locking Plant
  • Land-use change agreements
  • Wastewater Treatment Plant upgrades


Lake Rotoehu


Target 3.9

Result 3.95

Rotoehu has seen substantial improvements over the last five years and has been just above its target for the last two years. 

The actions of alum dosing and weed harvesting have contributed to these improvements in water quality while land-use change takes effect.

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


Lake Rotoiti


Target 3.5

Result 3.4

Rotoiti has been at its target for two years now thanks to the Ohau Diversion Wall and sewerage reticulation. 

It’s important to note that more reticulation is still required as well as sustainable improvements in Lake Rotorua for the long-term health of the lake.

  • Ohau Diversion Wall
  • Sewerage reticulation

Lake Okareka


Target 3.0

Result 3.3

Okareka’s water quality continues to remain stable, although still above its target. 

All actions for the lake have been completed.  The impact of land-use change will continue to be monitored to determine if further actions are required.

  • Sewerage reticulation of lakeside communities
  • Land-use change agreements




Target 2.7

Result 2.82

There was a slight decrease in the water quality result for Tikitapu, but the long-term water quality is stable.

  • Sewerage reticulation

Lake Okataina


Target 2.6

Result 2.69


Water quality continued to improve in Okataina and is close to the lake target.


  • Land-use and land management change
  • Investigation into impacts of native bush understory

Lake Rotoma


Target 2.3

Result 2.38

Water quality in Rotoma is stable and is close to its water quality target.


  • Main action of sewerage reticulation has not been completed.  Consultation for reticulation options has occurred.

Lake Rerewhakaaitu


Target 3.6

Result 3.43

Rerewhakaaitu is another lake that has been at its target for the second year. 

The Rerewhakaaitu landowners are being supported by the programme to develop and implement their own catchment plan. 

Landowners have done a tremendous job in reducing nutrient loss from their land and we are experiencing significant improvements in water quality as a result of their efforts.

  • 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 3.0

Tarawera’s annual water quality result was the same as last year, but is still significantly above its target.

Tarawera is presenting some challenges around quantifying nutrient inputs and therefore determining the actions needed to reach the water quality target.

  • Action plan in development

Lake Rotokakahi


Target 3.1

Result 3.63

Water quality has improved since the severe algal blooms of 2009, but still significantly above its target.



  • An Action Plan will be developed with lake owners.

Lake Okaro


Target 5.1

Result 4.49

Water quality significantly improved over the last year and recorded the best water quality result for the lake. 

Water quality does fluctuate in this lake and further investigation is needed.

  • In-lake phosphorus treatment
  • Constructed wetland
  • Riparian management


Lake Rotomahana


Target 3.9

Result 3.8

Water quality remains stable. 

  • Rotomahana has not yet reached the trigger point to need an action plan.