Lake Rotokakahi (the Green Lake) is adjacent to the Lake Tikitapu (Blue Lake) and can be accessed via Tarawera Road east of Rotorua. Rotokakahi is privately owned by local iwi and considered tapu or sacred, with no swimming or boating permitted on the lake. A small island on the lake is also of historical significance, and many people are buried there. The size of the lake is 440 Ha and the catchment has a total area of 1860 Ha. The average depth is 17.5 m and the deepest point is 32 m.
Rotokakahi means the lake of the shellfish "kakahi". While the Green Lake is now deserted and tapu, in days gone by it was heavily populated. The lake was known for its kakahi, an edible shellfish found in the lake's sandy bed. It is also famous for its island named Motutawa, the burial ground of many Maori ancestors Water quality is declining in Lake Rotokakahi and an Action Plan is being developed with the owners of the lake. The 3 year average TLI for the lake is well above its target of 3.1. In 2017 the TLI was 3.8. An Action Plan for Lake Rotokakahi is being developed in consultation with the owners of the lake to determine the nutrient load to the lake and what actions can be taken to improve the lake's water quality. There are complicated information gaps for this lake largely related to establishing nutrient sources and groundwater interactions.
Lake Rotokakahi was categorised as being in moderate ecological condition with a LakeSPI Index of 30% and is ranked 8th among all the Rotorua lakes. Lake Rotokakahi has been in a stable condition in recent years according to LakeSPI results.
Lake Rotokakahi has undergone one of the largest declines in lake condition as indicated by LakeSPI for any of the 12 lakes over the long-term (since full lake surveys began in 1988), with most change taking place prior to 2005. The LakeSPI Index has reduced from 52% in 1988 to only 30% in 2016, whilst the Native Condition Index has also declined significantly, largely due to a decline in deeper charophyte meadows over this time frame.