Regional lakes

Lake Kereta

On this page:

• About Lake Kereta
• How did this lake form?
• How healthy is Lake Kereta?
• Threats to Lake Kereta
• What is the ARC doing?
• Technical Publications

About Lake Kereta

Southerly aerial view of Lake Kereta

The low hills to the west are covered by scrubby native bush and a large area of exotic pine forest, while the low land to the east consists of pastureland. This provides most of the water to replenish Lake Kereta. Stock have unrestricted access to much of the eastern shore.

There are no obvious streams or rivers flowing into or out of Lake Kereta. The lake is filled mostly by groundwater and loses water by evaporation from the lake surface. Water also percolates out through the lake bottom if the groundwater level falls.

The very shallow water coupled with the large quantity of submerged and emergent aquatic plants make the lake into a natural waterfowl habitat. Australian little grebe, dabchick, black swan and paradise duck can be seen on the lake while bittern and fernbird have been recorded nearby.

Facts

How did this lake form?

The Kaipara South Head is a massive, ancient sand barrier that separates the South Kaipara Harbour from the Tasman Sea.

A long line of small interdune hollows run up the Kaipara South Head, parallel to the coastline. These interdune hollows are lower than the groundwater level so they fill up with groundwater to create small lakes. Lake Kereta is one of these interdune lakes.

How healthy is Lake Kereta?

Since 1998, the quality of the lake water has been monitored as part of our State of the Environment (SoE) Lake Water Quality monitoring programme.

The quality of any lake water is shown by its trophic state. This is very variable at lake Kereta, ranging between supertrophic (saturated in phosphorus and nitrogen with very high algae growth during calm, sunny periods) and mesotrophic (low to moderate amounts of nutrients and algae).

The water quality of Lake Kereta is currently supertrophic.

Threats to Lake Kereta

The most significant problems at Lake Kereta are the:

• exotic fish that have been recorded there (rudd, tench, koi carp and mosquito fish). This lake used to be popular with anglers as a major coarse fishery. However, large areas of the shoreline are now overgrown by invasive pest plants making access to the water difficult.
• spread of exotic pest plants around and within the lake, particularly Manchurian wild rice and hornwort.

Invasive plants

These were first recorded in 1950, when Manchurian wild rice and two other pest plant species had already formed a dense stand around the southern third of the lake. Drifting sand had destroyed the vegetation along the western shore.

In 1988 red and yellow varieties of Nymphaea sp. were noted.

Bladderwort was well established by 1993 and primrose willow was found along the western side of the lake.

By 1999 the Manchurian wild rice had spread to the marginal waters at the southern end of the lake. Water-lilies were also found in patches close to the shore.

A submerged exotic weed, hornwort, dominated the lake bed by 1999.

What is the ARC doing?

• The ARC is keeping the Manchurian wild rice around Lake Kereta under survelliance. It is designated as a Total Control Pest Plant under the Regional Pest Management Strategy. The strategy aims to prevent the plant from spreading outside the vicinity Lake Kereta.
• In 2006, the ARC commissioned NIWA to help develop a regional management plan for freshwater weeds and fish.
• The water quality is sampled once every two months as part of our State of the Environment (SoE) Lake Water Quality monitoring programme. Find out more about the Lake Water Quality monitoring programme.
• The ARC has operated and promoted the Environmental Initiatives Fund (EIF) since 1999. This supports individuals and groups to improve and care for the region's natural, cultural and physical environments. Around $500,000 is available annually. Find out more about EIF.
• We are working with the Department of Conservation (DoC) to support Weedbusters. This is a small-scale initiative fund for individuals or groups that want to eliminate pest plants. The funding helps to cover the cost of tools, herbicides, mulcher hire, greenwaste disposal and promotional activities. Find out more about Weedbusters.

Technical Publications

The ARC has a number of technical publications relating to this subject. Follow this link to see the full list of ARC technical publications.