Lake Taupō quick facts
- Lake Taupō was formed by a series of eruptions, the most recent of which – around 1800 years ago – blasted out about 60 cubic kilometres of earth, rock and mud, leaving a crater in the form we see today.
- More than 30 rivers and streams flow into the lake, with only one outlet – the Waikato River.
- The full name of the lake is Taupō-nui-a-Tia, which means the great cloak of Tia. Tia, one of the great fighting chiefs of the Arawa Canoe, is credited with discovering the lake.
- Lake Taupō is 30km wide and 40km long.
- The lake's deepest point is approximately 160 metres and it contains 59 cubic kilometres of water. The surface of the lake varies between a minimum of 355.85 metres and a maximum of 357.20 metres above sea level (depending on inflows and outflows – determined by hydro-electric generation).
- Lake Taupō is 622 square kilometres. Its catchment is about five times the size of the lake.
- The entire Lake Taupō catchment, including the lake, is 3487 square kilometres – 14 per cent of the Waikato region.
- Lake Taupō is home to many native plant species, at least 31 species of aquatic birds and several native and introduced fish, including koaro, the common bully, the common smelt, rainbow trout and brown trout.
- Catfish have been recorded in the lake since 1985. Catfish are a pest because they attack juvenile trout and feed on freshwater snails, koura, bullies and smelt.
- Oxygen weed, pondweed and hornwort are a growing problem in the lake. These water weeds spread rapidly and threaten the native plant species.
Lake Taupō's water quality
The water quality of Lake Taupō is generally excellent. Concentrations of the plant nutrients nitrogen and phosphorus are low, and so are the levels of microscopic algae whose growth they support. This is indicated by low concentrations of the plant pigment chlorophyll a. As a result, the water is clear and blue. In addition, the bottom waters of the lake are mostly well oxygenated.
Although blooms of potentially harmful blue-green algae have occasionally been observed in the lake, for example in March 2003, so far these have not been common. However, increases in the loads of nitrogen entering Lake Taupō were identified as a threat to lake water quality.
How land use affects Lake Taupō
More than 10 years ago, people became concerned about the effects of land use changes on the water quality of Lake Taupō. Some of the notable land use changes were:
- Government sponsored conversion of native forest and scrub to low intensity sheep and beef farms through the 1950s to 1970s
- a steady intensification of farming throughout the catchment
- the conversion of five sheep and beef farms to dairy farms.
All these were considered to be likely causes of the increases in nitrogen concentrations in rivers and streams in parts of the Lake Taupō region. Because of the age of ground water (median age ~40 y) it has taken some time for the effects of land use change in the 50s to 70s to become apparent in the lake and cause the effects the public began reporting in the late 1990s and 2000s. Calculations showed that about 94 per cent of the manageable nitrogen entering the lake came from areas of pasture in the catchment.
Water quality limits and measurement
Protecting Lake Taupō project’s aim, agreed with the public, has been to maintain the current water quality of the lake and prevent further decline. As a result, water quality limits have been set in the Waikato Regional Plan, which are to be met by 2080.
- Total nitrogen <70.3 (mg / m3)
- Total phosphorus <5.6 (mg / m3)
- Algae (chlorophyll a) <1,2 (mg / m3)
- Secchi disc clarity >14.6 (m)
To keep an eye on Lake Taupō’s water quality, Waikato Regional Council is operating a monitoring programme at the lake. A deep water site near the middle of the lake is visited every two to four weeks, and water samples are collected and field measurements made. The council has been doing this since 1994.
Click here for more information about the programme and its results.