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Shallow lakes of the Waikato region

The Waikato region’s shallow lakes are the largest remaining collection of their type in New Zealand. Many special native plants and animals live in and around them. A careful balance is needed between land use around these lakes to ensure their protection. Waikato Regional Council is working with landowners to protect shallow lakes in our region.

Photograph of Lake Mangakaware

On this page: Types of shallow lakes, Valuable natural resources, Stable lake conditions, Five stages of change, Caring for lakes , You can help, Find out more

Shallow lakes in the Waikato region generally have an average depth of less than three metres. Their surface areas range from less than one hectare (0.01 km2) to over 3,000 hectares (30 km2).

One of the smallest shallow lakes in our region is Lake Posa at Templeview, near Hamilton, with a surface area of 2.9 hectares (0.029 km2). The biggest shallow lake is Lake Waikare at Rangiriri, with a surface area of 3,440 hectares (34.4 km2). One of the deepest and clearest lakes is Lake Rotomanuka, south of Ohaupo, with a depth of eight metres.

Use our map to see the location of shallow lakes in the Waikato region.

Types of shallow lakes

Shallow lakes in the Waikato region are divided into four main groups:

Find out where these groups of lakes are located.

Valuable natural resources

Shallow lakes are often rich in plants and animals, and play an important role as wildlife refuges. Plants found near the edges of lakes are used to having ‘wet feet’ and include:

  • kahikatea
  • flax
  • cabbage trees
  • manuka
  • rushes and sedges.

They provide food and cover for birds and other animals, such as insects and fish living in the lakes. Waterfowl, such as grey duck and banded rail, rely on shallow lakes for food, shelter and breeding habitat.

Find out more about aquatic and wetland plants and animals.

Shallow lakes and their surrounding wetlands also play a role in storing extra water from the Waikato and Waipa rivers during floods. Without them, flood damage downstream to the lower areas of the Waikato would be more severe.

Stable lake conditions

Shallow lakes have two distinct stable states, generally depending on the amount of nutrients present in the water:

  1. Low nutrients - clear water, dominated by underwater (submerged) aquatic plants (macrophytes).
  2. High nutrients - murky (turbid) water, dominated by microscopic algae (phytoplankton).

Lakes with moderate nutrient levels are not stable in either state and can ‘switch’ from one state to the other, often suddenly. The factors causing a lake to change state are called 'pressures'. Pressures that cause a lake to change from clear to turbid water include:

  • increased nutrient levels entering the lake, for example from changing land use in the lake’s catchment
  • the introduction of plant or animal pests, which disrupt the lake’s ecosystem
  • water abstraction, which lowers the lake’s water level.

When these switches are reversed a lake can change from turbid to clear water, for example, when a lake’s nutrient levels are reduced.

The diagram below shows how pressures can change a clear lake from its ‘pristine’ state to a modified turbid state and vice versa.

Image showing lake stable states

Five stages of change

Lakes affected by increased nutrient levels generally go through five stages of change, during which the lake’s trophic status changes and water goes from clear to turbid. The five stages of change are:

  1. Pristine condition (natural state).
  2. Catchments are developed and land use changes.
  3. Increased plant growth – after a long period of nutrient enrichment.
  4. Blanketing of the water surface by floating plants.
  5. Collapse of large submerged aquatic plants (macrophytes).

1. Pristine condition (natural state)

Diagram of a lake in stage 1

  • Clear water (except peat lakes, which have naturally ‘stained’ water).
  • Lake floor dominated by aquatic plants (macrophytes).
  • Few microscopic algae (phytoplankton).
  • Bottom sediments are the main source of nutrients.

There is a balanced food web, supporting a wide variety of species, including:

  • macrophytes – large aquatic plants that live underwater (submerged)
  • phytoplankton – microscopic algae
  • zooplankton - animal plankton which feed on the phytoplankton
  • fish that feed on the zooplankton
  • carnivorous fish that feed on the smaller fish.

2. Catchments are developed and land use changes

Diagram of a lake in stage 2

  • Increased levels of nutrients enter the lake (onset of eutrophication).
  • Sediments lock up nutrients that are not taken up by plants.
  • Macrophytes respond to increased nutrient levels by growing more quickly and increasing in number.

3. Increased plant growth – after a long period of nutrient enrichment

Diagram of a lake in stage 3

  • Sediments can still lock up nutrients not taken up by plants.
  • Macrophytes no longer increase in number, however phytoplankton (microscopic algae) continue to increase.
  • Nutrient levels continue to increase.
  • Zooplankton numbers start to decline due higher numbers of fish that feed on them.

4. Blanketing of the water surface by floating plants

Diagram of a lake in stage 4

  • Sediments get saturated with nutrients and can no longer lock up additional nutrients.
  • Water contains large amounts of nutrients.
  • Phytoplankton grow even more quickly and in greater numbers.
  • Zooplankton continue to decline.

5. Collapse of large submerged aquatic plants (macrophytes)

Diagram of a lake in stage 5

  • Macrophytes die off as light and oxygen levels drop.
  • Phytoplankton are dominant and there are regular algal blooms.
  • Nutrient levels in the water are very high.
  • The variety of life in the lake is greatly reduced.
  • Oxygen levels in the water decrease.
  • Nutrients are released from the sediment into the water as oxygen levels drop.

Check out our diagrams showing how land use in a lake’s catchment affects water quality and wildlife.

Find out about algal blooms in the Waikato region.

Caring for lakes

Reducing the amount of nutrients entering a lake plays a key role in its protection. Waikato Regional Council works with local community groups and management agencies to care for our lakes and help restore them to their natural state. Find out about the restoration of Lake Ngaroto.

Many of our lakes have had high nutrient levels for many years, with nutrients stored in the sediment and the water. Scientists are looking at ways turbid lakes can be switched back to a clear, pristine state by experimenting with:

  1. Physical techniques, such as fountains, that increase the circulation of water and air within the lake to increase oxygen levels. This slows the release of nutrients from bottom sediments into the water.
  2. Chemical techniques to bind nutrients into bigger and heavier compounds that sink to the bottom of the lake. This reduces the amount of nutrients in the water, making less available for phytoplankton.
  3. Biological techniques that help to restore the natural balance of lake life. For example, the introduction of carnivorous fish, which feed on smaller fish, which feed on zooplankton. The resulting increase in zooplankton (animal plankton) helps to keep phytoplankton (plant plankton) levels low.

You can help

  • Keep stock away from lake edges.
  • Fence any lakes on your property.
  • Plant lake edges with native plants.
  • Find out about care groups and form a Lakecare group in your area.

Find out more

Find out more about our region’s riverine and peat lakes.

Find out about freshwater wetlands, and check out our tips for wetland management.

Learn about managing peat and check out our publications on freshwater issues.