Lake Rotoehu

The Situation


This picturesque 8.1 square kilometer crater lake is the smallest in a chain of three lakes northeast of Lake Rotorua. There are no major streams flowing either into or out of Lake Rotoehu. Water flows into the lake from springs in the lake bed and also seeps into Rotoehu from nearby Lake Rotoma to the east. Water exits the lake from a sinkhole in the northwest corner of the lake.



Average water depth is 10 m. The deepest part of the lake is 13.5 m. Numerous fingers and sheltered bays run off the main lake and are extensively used for recreation.


The shallow nature of Rotoehu, combined with nutrient runoff and relatively little water transfer, causes the lake to suffer from poor water quality. Blue-green algae blooms make the lake unsafe for swimming at times.


Rotoehu Lake authorities approached AWT to discuss treatment options. PondPerfect was chosen as one of the treatment options. PondPerfect is a non-toxic, live bacterial product designed to restore a proper balance between algae, sludge, and bacteria in eutrophic lakes.


Test Site


To facilitate a test of the effectiveness of PondPerfect, a small finger-shaped cove in Omarupoto Bay was chosen as a test site. The test site has the advantage of relatively stagnant, non-flowing water. This allowed use of the finger cove as a test site, while the neighboring water could be used as control.