Lake Rotomahana is located south east of Lake Tarawera. Lake Rotomahana was the site of the geothermal "Pink and White Terraces", once considered the eighth wonder of the natural world. The terraces were destroyed in the 1886 Tarawera eruption, which also substantially altered the lake. Today, it is the deepest of the Rotorua lakes and is said to contain the purest strain of rainbow trout in the world. there is no public access to this lake. Lake Rotomahana is 900 Ha in size and its total catchment area is 8370 Ha. The average depth of this lake is 60m and at its deepest point it is 125 m.
Rotomahana means "warm lake". Prior to the Tarawera eruption, this lake comprised two smaller lakes - Lake Rotomahana (warm) and Lake Makariri (cold). The long-term water quality trend for Lake Rotomahana is stable. No actions have been undertaken as Lake Rotomahana has not triggered the need for an Action Plan. The Lake will continue to be monitored and if this changes an Action Plan will be developed in consultation with the community.
The TLI for Lake Rotomahana is around 4 and the target level is 3.9.
Prior to 2013 Lake Rotomahana was the top ranked Rotorua Te Arawa Lake according to LakeSPI. For many years it was stable, but showed a deterioration over 2011 to 2013, due to the establishment of Egeria and Hornwort, two of New Zealand's worst aquatic weeds.In 2015, these weeds diminished in their abundance and lake condition has improved. From the 2017 survey, Lake Rotomahana is the highest ranked lake in the rotorua region and has been categorised as being in high ecological condition. No Hornwort was observed from the LakeSPI sampling sites.