Project Whakahaumanu
November 1, 2021
Rotoiti Aquatic Weed Spraying
November 3, 2021
28 October 2021
Lakes Water Quality Society Policy Brief for Lake Rotoiti.
Dated 14 June 2021
Required Action
* Restoration of native flora by suppression and then eradication of lake weeds
* Suppression and then eradication of Catfish
* Enforcement of the Rule to prevent further pest incursions(fish and weeds) by requiring certification of a clean boat before launching.
* Maintenance of the Ohau Channel Diversion wall.
* New rules to prevent excess erosion during forestry harvesting.
* Completion of sewerage reticulation at eastern end.
Background
Lake Rotoiti is situated to the northeast of Rotorua and is bounded by SH 33(Tauranga) on its western side and SH 30(Whakatane) on its southern shores. It is the most popular trout fishing and boating lake in the District. The western end is a drowned river valley and has a splendid variety of small bays and inlets, on the northwest side many have been developed with lakeside homes. The eastern end of the lake is a large very deep caldera with lakeside properties along the State Highway extending down to Hinehopu and magnificent bush clad cliffs on the opposite side.
The full name of the lake is Te Rotoiti-kite-a-Īhenga, which in Maori means "The Small Lake Discovered By Īhenga". Legend says that the lake was named as such because when Ihenga first sighted it he only saw a small part.
Statistics are:
Size 3400 ha
Length 15km
Width 2.6km
Catchment 12,160 ha
Average depth 31m
Max depth 93.5m
Elevation 279m
Formed 8500 years ago
Target TLI 3.5
TLI 2019/20 3.7
TLI 2016 3.8
Target LakeSPI 100%
LakeSPI 2017 18%
Chronology
1960s- Introduction of lagrosiphon and other lake weeds, rapidly spread colonising much of the littoral zone
1970s- Significant land use change from farming with substantial planting of plantation pines
2003- Lake had several big blue-green algae blooms that became a regular feature.
2006- First Stage of sewerage commissioned for Mourea, ultimately extended to Otaramarae
2008- Ohau Diversion Wall erected as the main intervention to restore the health of the lake. Nutrients from Rotorua catchment diverted directly down the Okere Arm to the Kaituna River.
2016- Brown Bullhead Catfish confirmed in Te Weta Bay, initially confined by a cordon but within 2 years was abandoned. Now spread throughout the entire lake but most abundant in the shallower western end. Spread up the Ohau Channel into Lake Rotorua. Suppression netting programme run by BOPRC. Educational programme “Catfish Killers” run by TALT. Sterile male control programme commenced in 2021, likely to be a decade before significant reductions achieved.
2019- Endothall trial to assess eradication of hornwort and lagrosiphon
2020- Adoption of Rule 10 reducing nutrients in the Rotorua Catchment
2021- Eastern sewerage due to be finished completing the sewerage to the entire lake.
2021- Increased suppression by LINZ spraying of lake weeds for recreational activities
More information on the Lakes Water Quality Society is available here.