The lakes of Aotearoa New Zealand

Aotearoa has world-famous lakes – for example, Lakes Taupō, Rotorua and Wakatipu – but there are a huge number tucked away that most of us probably don’t know about. Believe it or not, New Zealand has about 3,800 lakes larger than 1 hectare (the size of a rugby field)! Many of these lakes are in remote locations or out of sight on private land.

A lake is defined as an area or basin filled with water and surrounded by land. This generic description may be accurate but it makes one lake sound much like another. In fact, lakes vary widely depending on their origins and catchment areas.

Lake origins

The unique geography of Aotearoa New Zealand is responsible for the incredible diversity of lakes in this country. Mountains, volcanoes and our extensive and complex coastlines have all had a part to play in creating the thousands of lakes throughout the motu.

Te Waipounamu South Island is home to numerous glacial lakes. It is estimated that about a third of the island was once covered by ice. Ancient glaciers – huge masses of ice – slowly moved from the mountains to the lower lands. Ice is very effective at wearing away rock, and the glaciers forged large, steep valleys. The rocky debris pushed along by the front of some glaciers created natural dams and lakes formed in the basins and hollows. Glacial lakes like Takapō Lake Tekapo and Lake Pukaki contain glacial flour – extremely finely ground rock particles – which gives the lakes a turquoise colour. In recent times, glacial lakes have formed at the terminus (edge) of big glaciers in Aotearoa as the ice more rapidly melts. Tasman Lake began as small meltwater ponds in the 1970s, and it is now more than 7 km long.

Te Ika-a-Māui North Island does not have glacial lakes but it does have volcanic lakes. Past eruptions in the Taupō Volcanic Zone and Auckland Volcanic Field have created enormous calderas, which filled with water to form lakes like Taupō and Rotorua. Other lakes like Pupuke Moana formed in dormant craters.

Lakes are also formed by other natural processes:

• Riverine lakes form in depressions on floodplains or when river channels move.
• Dune lakes form by wind-blown sand deposits or within old sand dune systems.
• Shoreline or coastal lakes form when a barrier bar of land (often called a spit) separates fresh or brackish water from the sea.
• Peat lakes form when edged or surrounded by peat – the remains of wetland plant vegetation that slowly builds up over time.

Lakes can also be formed by artificial means. These are usually created when rivers are dammed for power generation and water supply.

Lakes are surrounded by a catchment

Lakes are part of a wider ecosystem known as a catchment – the area that collects all the water that drains to the lake. Catchments are also known as watersheds or drainage basins.

Natural physical, chemical and biological factors affect the condition of a lake. Physical factors include temperature, light and wind, while chemical factors include pH and nutrients like nitrogen and phosphorus. Biological factors include the bacteria, fungi, plants and animals that live in the lake and in the catchment area. Each of the factors is intertwined – for example, the water in a peat lake is mildly acidic and low in nutrients, so the plants and animals that live in the peat lake have adapted to these conditions.

While natural events like drought, storms or even earthquakes affect lakes, humans have an overwhelming influence on catchment health. Land-use activities – such as the burning or removal of native vegetation to create agricultural or urban areas – influence the amount of water, sediments, nutrients and contaminants that enter a lake. Excess nutrients can upset the balance of plant growth, which in turn affects water clarity and oxygen levels.

Coastal and lowland lakes in Aotearoa tend to be located in catchments containing high levels of agricultural, urban or other types of human development.

Lakes and wellbeing

Lakes and other freshwater environments are important to our identities in Aotearoa New Zealand. Lakes are important for recreation and good for our physical and mental wellbeing. In te ao Māori, the human and non-human worlds are indivisible. There are kinship relationships and responsibilities towards roto (lakes) and other natural features. Lakes are also important for mahinga kai.

Conservation and restoration

Lakes380 – Our lakes’ health: past, present, future notes that prior to its scientific study, environmental data existed for fewer than 5% of our 3,800 lakes, and these datasets typically covered less than 20–30 years. Land, Air, Water Aotearoa (LAWA) notes that only 127 of Aotearoa New Zealand’s lakes are regularly monitored for concentrations of total nitrogen and total phosphorus, water clarity and algae levels. These measues are used to determine overall lake condition.

Lake monitoring enables scientists to obtain an overview of the health of a lake and to look for changes to its state over time. It’s very important that iwi, local groups, regional councils and others have this knowledge for the ongoing conservation of healthy lake ecosystems. This knowledge can also inform lake restoration and help prioritise protection.