Riverine lakes

The Waikato region’s riverine lakes are part of an extensive wetland system that includes Lakes Whangape, Waahi, Waikare and the internationally significant Whangamarino Wetland. The lakes are linked to the Waikato River, New Zealand’s longest river.

This wetland system is one of the most important freshwater habitats in New Zealand.

On this page:

What are riverine lakes? •
An important habitat •
Threats •
What we're doing

What are riverine lakes?

Our riverine lakes were formed when alluvial deposits¹ diverted the original path of the Waikato River, leaving blocked valleys and tributaries. Most of these riverine lakes still remain linked to the Waikato River.

The Waikato’s floodwaters determine the physical, chemical and biological characteristics of these riverine lakes.

Riverine lakes are a valuable habitat for many unique birds, fish and plants. There are 14 riverine lakes in the Waikato region.

Lake Whangape Lake Waahi Lake Waikare

An important habitat

Riverine lakes support a variety of waterfowl including several threatened native species, for example:
- Australasian bittern
- banded rail
- grey duck
- grey teal
- marsh crake
- New Zealand dabchick
- New Zealand shoveler
- spotless crake
Brown teal were once present, but are now believed to be regionally extinct.

Although some of the wetland birds are sedentary (staying in one place to defend individual territories), most are very mobile. Many birds move between lakes and wetlands as food and nesting requirements change with seasonal variations in water levels. The large lakes are especially important as a refuge for moulting birds that are growing new flight feathers.
Native fish found in the lakes include:
- common smelt
- grey mullet
- longfinned eel
- shortfinned eel
- whitebait (Galaxiid species).
Native fish such as the longfinned and shortfinned eel, grey mullet and whitebait species also move between the swamps, lakes, river and the sea, depending on their particular life cycles. Populations of the endemic black mudfish (only found in New Zealand) can be found in wetlands next to riverine lakes.
Riverine lakes support a number of endangered plants along their margins that are intermittently wet. Several of these species form low growing water-loving communities (called turf communities) that develop in areas exposed from summer to autumn, but are under water (submerged) during winter. Previous studies of turf communities around Lake Whangape found:
- the ‘critically endangered’ grass Amphibromus fluitans
- the largest known population of the native annual sedge Fimbristylis velata
- Regionally significant populations of the herb Pratia perpusilla and the sedge Carex gaudichaudiana.

Threats to our riverine lakes

A botanical survey in 1870 reported that Waikato riverine lakes had high water clarity with many different kinds of native underwater plants. Surrounding the riverine lakes the original catchment vegetation was mixed podocarp-broadleaf forest with dense stands of kahikatea forest in the low lying valleys.

Since human settlement, clearance of the original forest and wetland vegetation and the switch to agricultural land use has substantially changed the condition of the lakes. Many of the lakes are now turbid (cloudy) and can’t support submerged plants.

Check out our Extent of Native Vegetation indicator to find out more about changes in the region’s vegetation cover since 1840. You can also view our map showing past and present wetland coverage in the Waikato region.

Riverine lakes are naturally shallow and exposed. In the past they were less affected by wave disturbance because:

there was less sediment entering the lakes - due to dense vegetation cover around the lake edge
they had communities of submerged aquatic plants that helped dampen the stirring effect of waves.

However, today vegetation clearance has increased sediment loads into the lakes and reduced water clarity. Submerged plants can’t survive in murky water and so die out. In addition:

Stock grazing and trampling along lake edges reduces plant cover and prevents the establishment of a buffer of vegetation that helps to reduce nutrients entering the lake.
Fertiliser, stock urine and dung increase nutrient levels in the lakes, causing algal blooms.
Invasive plants such as grey and crack willow have displaced native sedges and rushes that once grew along the lakes’ edges. Introduced oxygen weeds largely replaced submerged native plants. The oxygen weed has since died off (due to lack of light and oxygen, increased nutrient levels and grazing by swans and fish such as rudd).
Introduced koi carp and brown bullhead catfish stir up the lake sediments and uproot aquatic vegetation, affecting water quality. The lakes and remaining nearby wetlands are highly modified environments, dominated by introduced plants.

What we're doing

Waikato Regional Council supports Lakecare groups in restoring the natural vegetation around lake edges and wetlands through fencing and planting.
Weirs have been installed to maintain water levels in the lakes and wetlands. Lakes with water level control structures include Waikare, Whangape, Waahi, Kimihia and Hakanoa. A large rock rubble weir has also been installed in the Whangamarino River to protect water levels within the Whangamarino Wetland.
Waikato Regional Council and the Department of Conservation provide advice and information about how to minimise the risk of spreading weeds and pest fish from one lake to another.
A fish pass has been constructed at Lake Waikare to allow the movement of eels, mullet, inanga and smelt into the lake.
The Regional Pest Management Strategy restricts the sale and movement of pest fish around and into the region.
Waikato Regional Council controls the discharge of pollutants (for example sediments and nutrients) to waterways through the Regional Plan.
A resource consent is required for wastewater to be discharged to a water body (such as from dairy farms, sewerage or factories).

Footnotes

Sediments deposited by water, such as sand and silt.