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Regional lakes

Lake Kuwakatai

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About Lake Kuwakatai

The lake's orientation means that it is exposed to the prevailing winds, but in calm conditions in summer, the surface water can get much warmer than the deeper bottom water. This creates distinct layers of water in the lake, each at a different temperature; an effect known as thermal stratification.

This occasional thermal stratification means the oxygen-rich surface water is not mixed with the deeper water, which becomes starved of oxygen (anoxic). The decaying plant and organic matter in the deeper water uses up all the oxygen as they decompose and release nutrients. When the waters start to mix again, these nutrients can produce algal blooms.

There are no obvious streams flowing out of the lake, but a small stream flows into the head of each branch during wetter periods. The lake water comes from these occasional streams, direct rainfall, and seepage through the lake bottom from the surrounding sandy land. The water is fairly turbid.

Most of the lake is surrounded by scenic rural pasture and there are several dairy farms in the catchment area.

Facts

Location guide  At the northern end of South Kaipara Head, along the west coast of the North Island, New Zealand. See location map of Lake Kuwakatai
Surface areaAbout 29 hectares
Maximum depthAbout 19m
Catchment areaAbout 410 hectares
Type of catchmentPasture (85%)
Exotic forest (4%)
Native forest/scrub (11%)
Urban (none)
Surface water temperatureAverage 17.8°C
Number of sampling sitesOne site, but water samples are collected at two different depths.

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 interdune hollows and valleys runs up the Kaipara South Head. Lake Kuwakatai is a dune lake that formed when two of these valleys were blocked by sand dunes and drowned as water accumulated in the valleys.

How healthy is Lake Kuwakatai?

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.

Since 2005, the water quality at Lake Kuwakatai has been supertrophic (fertile, saturated in phosphorus and nitrogen, with very high algae growth and blooms during calm and sunny periods).

 Microptrophic Oligotrophic MesotrophicEutrophic Supertrophic Hypertrophic
2006/07   

 

x

 
2005/06   

 

x

 

Threats to Lake Kuwakatai

The most significant problems at Lake Kuwakatai have been, or currently are the:

  • high level of nutrients (phosphorus and nitrogen) from the surrounding catchment area which is used mostly for pasture.
  • invasive submerged weed, hornwort. This is the worst invasive weed in the country and can wipe out all other types of submerged vegetation. At present, hornwort is the only species of submerged vegetation present in Lake Kuwakatai and was first discovered in 1999.
  • Four types of pest coarse fish have been introduced into this lake.

What is the ARC doing?

  • 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.

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.

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