Lakes

The quality and overall health of the region's lakes is dependent on a variety of factors. Several key pressures have been identified as potential drivers of changes in water quality in Auckland’s lakes including, but not limited to, catchment land cover type, pest fish, invasive plant species, internal nutrient loading, and a changing climate.

Our Monitoring Programmes

Auckland Council has two separate methods for monitoring the health and ecological state of the lakes within the region. The first of these monitoring programmes is the water quality programme which is a monthly monitoring programme that measures a suite of water quality variables to evaluate changes over time. These variables are measured by taking physical water samples at the deepest part of the lake, from both the surface and bottom waters of the lake. Samples are analysed for concentrations of nutrients (e.g., nitrogen and phosphorus), algae and sediment. Each lake is also tested for concentrations of E. coli and cyanobacteria, which can indicate the level of faecal contamination and toxin producing cyanobacteria, which are both of risk to human health.

In situ water quality readings are taken using a sensor to measure the temperature of the water, the concentration of oxygen in the water, pH, conductivity, and turbidity, at every one metre depth until we reach the bottom of the lake.

The second monitoring programme is used to assess ecological condition by surveying submerged macrophytes (plants) using the LakeSPI method. This assesses the percentage of native and invasive vegetation within a lake and will be undertaken every three years.

The most recent report on the state and trends of water quality in four of the historically monitored lakes in Auckland can be found here.

There are eight lakes in the Auckland region that are part of the Lakes380 project (https://lakes380.com/region/auckland/). Lakes380 is a large study of New Zealand lakes by collecting and analysing water samples, lake bottom sediment samples and lake sediment cores from about 10% of our 3,800 lakes (>1 ha). A suite of scientific tools are being used to determine the current and historic health of each lake. 

Management

Management in these lakes over recent times have included pest fish management including; over-fishing to improve water clarity, fish community surveys, and invasive weed management through the introduction of grass carp. Some lakes have had restoration work including stock exclusion and planting of the riparian margins.

Further work to guide management strategies has included an assessment of the recreational use and public knowledge around freshwater biosecurity, exploratory research into nutrient loading, and the effect of fish grazing on native charophyte restoration. Future management is anticipated in Lake Rototoa and Lake Tomarata as part of council’s Natural Environment Targeted Rate (NETR) work programme.