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The Waikato region has more than 100 lakes, ranging from small ponds to the largest lake in New Zealand, Lake Taupo. Waikato Regional Council is looking at ways to protect Waikato’s lakes and restore those with poor water quality.

What affects lakes?

Demand for farmland and urban development close to water has meant that most of our lakes are now much smaller and shallower than they were in the early 1900s. Some lakes have been completely drained and turned into pasture.

Lakes tend to collect pollutants over time because their waters are still, unlike rivers where moving waters carry pollutants away. More intensive use of land in lake catchments means many lakes now receive more nutrient and sediment loads than in the past. Nutrients encourage nuisance plant growth, such as water weeds and algal scums. 

Measuring water quality in our lakes

Waikato Regional Council monitors the water quality of lakes using four main trophic indicators:

  • Secchi depth - measuring water clarity
  • Chlorophyll a - measuring the amount of algae in the lake
  • Total Phosphorus - measuring the amount of phosphorus available for plant and algal growth
  • Total Nitrogen - measuring the amount of nitrogen available for plant and algal growth.

The five trophic states determined by these indicators are:

  • Oligotrophic lakes are clear and blue, with very low levels of nutrients and algae. Lake Taupo is an oligotrophic lake.

  • Mesotrophic lakes have moderate levels of nutrients and algae. Lake Taharoa is a mesotrophic lake.

  • Eutrophic lakes are green and murky, with higher amounts of nutrients and algae. Lake Rotoroa (Hamilton Lake) and Lake Rotomanuka are eutrophic lakes.

  • Supertrophic lakes are fertile and saturated in phosphorus and nitrogen, often associated with poor water clarity. Excessive phytoplankton growth can occur in ideal conditions - when there's a calm, hot and sunny period of a few weeks.

  • Hypertrophic lakes are highly fertile and supersaturated in phosphorus and nitrogen. They have excessive phytoplankton growth which contributes to poor water clarity, poor suitability for recreational uses, and restricts the habitat for desirable fish. Lake Hakanoa and Lake Ngaroto are hypertrophic lakes.

Looking after Waikato’s lakes

Waikato Regional Council's land and river-based works and services are designed to protect the lake water quality and the land surrounding them from the effects of erosion. The work done includes:

  • soil conservation fencing
  • soil conservation planting
  • land retired from grazing use
  • erosion control flumes
  • stock water supply systems
  • stock access-ways and bridges.

Waikato Regional Council also works with community groups and other management agencies to set water levels for peat lakes to help protect these unique ecosystems for the future. Peat lake ecosystems are easily damaged by over drainage of neighbouring land.

There are now community caregroups looking after several of our peat and lower Waikato River lakes in the Waikato region. Lake Ngaroto is also the focus of a major rehabilitation project.