Lake Ngaroto

Lake Ngaroto is the largest of the Waipa peat lakes. It is located south of Hamilton city and north-west of Te Awamutu. Lake Ngaroto has poor water quality, however a major effort has been launched by Waipa District Council to return this lake to a more natural state, surrounded by native vegetation.

Lake Ngaroto is located 19 kilometres south of Hamilton city, and approximately eight kilometres north-west of Te Awamutu. The lake has a surface area of about 108 hectares. It has a maximum depth of four metres and an average depth of less than two metres.

Lake Ngaroto is the largest of the Waipa peat lakes. The lake catchment is mainly pastoral.

Results from water quality monitoring undertaken by Waikato Regional Council show that Lake Ngaroto is hypertrophic. It has:

• very high levels of nutrients
• high levels of microscopic algae (phytoplankton)
• high levels of suspended sediment
• low water clarity.

The National Institute of Water and Atmospheric Research (NIWA) found no submerged aquatic vegetation during the last vegetation survey in 2003.

Check out our Nutrient Enrichment of Shallow Lakes indicator and its data for Lake Ngaroto.

Waikato Regional Council collected water quality samples monthly between October 1995 and December 2001. There has been no change in the nutrient status of Lake Ngaroto during this time.

Monitoring results found:

• no changes in chlorophyll a, total phosphorus or total nitrogen
• a decrease in secchi depth (water clarity) of around 10 centimetres per year.

Results show seasonal patterns in water quality, with:

• water clarity and total nitrogen highest in winter
• total phosphorus and chlorophyll a highest in summer.

Future monitoring by Waikato Regional Council will show any improvements in water quality as a result of the restoration project.

Waipa District Council started a restoration project in 1995, creating marginal strips of land around the lake that could be fenced and planted.

The whole lake boundary is now fenced and well over half of the lake edge is planted. Considerable effort has been made to plant native species grown from locally sourced seed.

Weed control is an important part of the restoration project. While some weeds have been cleared, others are being left if they can be overtaken by the native plantings. Several thousand manuka seedlings had grown enough within a year to begin shading out weeds like blackberry. Kahikatea trees planted among stands of unwanted willows are expected to shade out and replace the willows within the next 40 years.

Increased sediment input to the lake has made it shallower and more turbid, while nutrients washed in from the surrounding land encourage nuisance plant growth. Sediment and nutrient traps have been constructed to help the lake's recovery.

Waipa District Council has monitored the lake's water quality to establish a benchmark, this means that future monitoring can tell how the plantings and sediment and nutrient controls improve water quality.

Newly planted native species will encourage more wildlife (including native birds) back to the area. The lake is also used for recreation, and the boardwalk built by Te Awamutu Kiwanis Club greatly enhances access to and around the lake.

The restoration project received a wetlands conservation award from the Minister of Conservation in February 2000, and was nominated for a Ministry for the Environment Green Ribbon Award in 2002.