Lake Horowhenua's first report card not good news

Lake Horowhenua's health is still below national standards.

The first report card on the health of Lake Horowhenua is in and it is not good. The lake's health does not even reach the minimum standards set in New Zealand's National Policy statement for Freshwater Management 2014. But things can only get better from here, as work has begun on issues identified in the 2013 Lake Horowhenua Accord Action Plan 2014-2016.

The lake is still considered to be supertrophic. The trophic index measures the water clarity, chlorophyll content, phosphorus and nitrogen content on a scale of 1 -7, 7 being the worst. Lake Horowhenua is classed as 6.7 and has slowly been climbing since 2014. The situation was at its worst in 2009, when it went off the scale, reaching 7.1. From 2010-2013 the lake's water quality wasn't monitored.

E.coli levels are at their worst on the lake edges, representing a risk to human and animal health. In the centre of the lake levels are considered safe, perhaps due to UV radiation.

Restoration work in progress, such as sediment traps and weed harvesting, is expected to improve the water quality in the next few years. Dairy farms, cropping farms and horticultural businesses surrounding the lake now all have plans in place to deal with nitrogen and sediment run-off. NIWA scientist Dr Max Gibbs is projecting the lake will move up a notch or two on all nutrients.

Main issues are nutrient run-off, phosphorus and nitrogen, sediment, e-coli, and cyanobacteria.

Dr John Roygard of Horizons Regional Council says the report card provides a snapshot of the current situation.

"The report card covers the ecosystem health, how the Lake health affects recreational activities, where it sits on the trophic level index, its pre-European history, and key actions that have been completed since the signing of the Lake Horowhenua Accord (He Hokioi Rerengatahi) in 2013.
"This means there is a clear stake in the ground to reflect on as we move forward and make progress," he says.

Horowhenua Lake Accord chairperson, and chair of the Lake Horowhenua Trustees, Matt Sword explains further that the report card is one of the outputs for the project, Te Kakapa Manawa o Muaūpoko - The heart beat of Muaūpoko.

"This report card is one of 13 projects being undertaken as part of Te Kakapa Manawa o Muaūpoko which is funded through the Ministry for the Environment's Te Mana o te Wai Fund. It has a total budget of $1,161,961 with a contribution from central government of $971,660, investment by the Lake Trust and funding and technical support from both Horizons and Horowhenua District Council."

"The Lake Report Card will be updated annually to indicate what progress we are making against key indicators of Lake health."

"A major project to limit the amount of nutrients entering the Lake has been the Arawhata sediment trap, which has recently been completed," says Dr Roygard.

"The sediment trap is estimated to reduce the annual load of sediment input to Lake Horowhenua via streams by approximately 25 per cent and the annual load of phosphorus by 30 per cent. Another major intervention to improve the Lake's suitability for recreation is the lake weed harvesting project, which is planned to start in 2018 following the High Court's decision to allow the harvesting operation to go ahead."

So far 19kms of fencing has been achieved, seven community plantings took place, with 7765 native trees planted along streams and lake, two fish barriers have been installed and a sediment trap on the Arawhata Stream.

Research has established that 12 species of native fish live in the lake as well as three introduced species of fish.

Next year a major weed harvesting operation is to take place, which will improve water flow, diminishing chances for sediment to settle on the bottom of the lake.

The Lake Horowhenua report card can be found at www.horizons.govt.nz/managing-natural-resources/parks-projects/lakes-rivers.