Lake Rotoiti

Lake Rotoiti

Lake Rotoiti

Ihenga came inland to explore the area. His dog Potakatawhiti disappeared for some time and on return, vomited up whitebait. Ihenga then realised he was near water. He landed on the shores of the lake which, because of the size of the particular bay, he was deceived into thinking the lake was small. He called it Lake Rotoiti, or Te Roto-Whaiti-i-kite-ai-a-Ihenga-i-Ariki-ai-a Kahumatamomoe

Lake Rotoiti is a relatively large lake and a popular location for boating and fishing. It is linked to Lake Rotorua via the Ohau Channel. This means that the quality of the water in Lake Rotorua has a significant effect on Lake Rotoiti. Much of the work being done to improve Lake Rotorua is also aimed at improving water quality in Lake Rotoiti.

In July 2008 a diversion wall was constructed that prevents water that has a high nutrient content from flowing directly into Lake Rotoiti. As a result more than 70 percent of the nutrients that were flowing into Lake Rotoiti have now been diverted down the Kaituna River. The resource consent for the Okere Gates also requires them to be operated to ensure water quality in Lake Rotoiti, by preventing backflow in to that lake.

At a glance  
Lake size: 3400 ha
Catchment area: 12160 ha
Elevation: 279 m
Average depth: 31 m
Deepest point: 93.5 m
Formed: 8500 years ago
Drains to the Kaituna River; and to Lakes Rotoehu and Rotomā via subsurface flow  








Water Quality Status

There are two actions for Lake Rotoiti and both are now complete, with the exception of a small amount of sewerage reticulation at Gisborne Point and Hinehopu, now scheduled to be completed along with the reticulation of Lake Rotomā in 2018-2019. 

The Programme’s completed actions including the Ohau Diversion Wall and sewerage reticulation have improved water quality in Lake Rotoiti dramatically from its crisis point in the mid-2000’s.  Lake Rotoiti water quality is now stable at or around its target TLI of 3.5, based on a 3 year rolling average.

The long term plan for Lake Rotoiti is to eventually remove the Ohau Diversion wall, once Lake Rotorua water quality has sustainably improved, enabling the waters to mix again.

Catchment Map

Click here for image of map

Target and Results

To meet community expectations Lake Rotoiti needs a reduction of 130 tonnes of nitrogen and 19 tonnes of phosphorus. 

Water quality in Lake Rotoiti is affected by Lake Rotorua.  The Ohau Diversion Wall is diverting Lake Rotorua's nutrient rich waters away from Lake Rotoiti.  This intervention is protecting water quality in Lake Rotoiti while actions are implemented to improve Lake Rotorua's water quality.

Water Quality target  


2017 result


2016 result








The 2015 TLI for Lake Rotoiti was well above the target TLI due to a long hot summer. However, lake water quality needs to be considered by a rolling average rather than annually to get a true picture of water quality conditions. This is because annual readings can be influenced by one off climatic conditions. The 3 year rolling average TLI for Lake Rotoiti is around its target of 3.5 and the lake water quality is considered stable.



Actions and achievements

Lake Rotoiti water quality is stable.  The lakes nutrient reduction targets have largely been met as detailed below.



Achieved as at June 2016


Ohau Diversion Wall

150 T N

150 T N

15 T P

The Ohau Diversion Wall has successfully stopped nutrients entering the lake from Lake Rotorua via the Ohau Channel.

Sewerage Reticulation

8.5 T N 1.9 T P

5.84 T N

0.48 T P

Lakeside communities in Okere, Otarmarae, Whangamarino, Mourea and Okawa Bay have been reticulated. 

Hinehopu/Gisborne Point sewerage scheme is still to be completed to achieve the total reduction.

Action Plan

Lake Action Plans direct what steps need to be taken to improve lake water quality to meet community expectations

Read Lake Rotorua & Rotoiti Action Plan