Te Whanga Lagoon

Te Whanga Lagoon is a large lagoon in the northern part of Chatham Island, covering around 160 km² - around one fifth of the island. The lagoon is surrounded by sand dunes along its northern and eastern edges, while the western shoreline is lined with cockle shell beds and long ridges of sand and shells.

The lagoon is brackish, with salinity levels reaching or exceeding 50% seawater. It naturally opens to the sea via the Hikurangi Channel, a sand barrier beach on the east coast. However, the outlet frequently becomes blocked, and it is often necessary to mechanically open if the water level gets too high and risks damaging roads or farmland.

Many streams and lakes flow into the lagoon, which holds great cultural and ecological importance for the community.

While the southern basin remains in relatively good condition, the northern and central basins are showing signs of nutrient stress.

The Trophic Level Index (TLI) results presented are from the monitoring site in the central basin at Airbase Road.

Lake Summary

Lake size

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Scientific data for this lake

This dashboard shows information on the data collected by the regional councils and unitary authorities for two indicators of lake water quality and ecological condition: TLI (Trophic Level Index) and LakeSPI (Lake Submerged Plant Indicators). Select an indicator to see the historical results.

Water Quality

Trophic Level Index (TLI)

The TLI score is an indicator of lake health and is determined from a suite of water quality measurements.

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Trophic Level Index (TLI) history for this lake

The TLI score for a lake is calculated from four water quality measurements – chlorophyll a, total nitrogen, total phosphorus and water clarity. If water clarity is unavailable, TLI is calculated using the other three water quality measurements. A higher score indicates poorer water quality.

View a factsheet on TLI

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TLI history for Te Whanga Lagoon

Year

What do the icons mean?

Very good water quality. Trophic Level Index of 0-2. Microtrophic lake conditions.

Good water quality. Trophic Level Index of 2-3. Oligotrophic lake conditions.

Average water quality. Trophic Level Index of 3-4. Mesotrophic lake conditions.

Poor water quality. Trophic Level Index of 4-5. Eutrophic lake conditions.

Very poor water quality. Trophic Level Index of greater than 5. Supertrophic lake conditions.

Not assessed.

TLI history for Te Whanga Lagoon data table

Year	TLI Score

Year	TLI Score

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Ecological Conditions

Lake Submerged Plant Indicators (LakeSPI)

The LakeSPI status describes the ecological condition of the lake and is based on plants present.

LakeSPI data provided by NIWA

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LakeSPI history for this lake

LakeSPI (Lake Submerged Plant Indicators) is a method of characterising the ecological condition of lakes based on the composition of native and invasive plants growing in them. A higher LakeSPI percentage result is associated with better ecological health:

LakeSPI	N/A
LakeSPI	{{spiData.details.Value}}%

The overall LakeSPI score is calculated using a Native Condition Index ('good' plants) and an Invasive Impact Index (introduced, non-native plants):

Native Condition	N/A
Native Condition	{{spiData.details.NativeIndex}}%

Invasive Impact	N/A
Invasive Impact	{{spiData.details.InvasiveIndex}}%	NA

A higher Native Condition value indicates better ecological condition, but a higher Invasive Impact value indicates invasive plants are negatively impacting native plant communities.
View a factsheet on LakeSPI for more information on these indicators.

LakeSPI
Native Condition
Invasive Impact

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LakeSPI history for Te Whanga Lagoon

Year

What is this graph showing me?

This graph is displaying the overall LakeSPI score over time. The results denote the ecological condition of the lake.

Excellent ecological health. A LakeSPI score of 75-100%.

High ecological health. A LakeSPI score of 50-75%.

Moderate ecological health. A LakeSPI score of 20-50%.

Poor ecological health. A LakeSPI score of 0-20%.

Non-vegetated. A LakeSPI score of 0% (there are no plants present).

No data available.

LakeSPI history for Te Whanga Lagoon data table

Sample Date	LakeSPI Status	LakeSPI %	Native Condition Index %	Invasive Impact Index %

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NIWA LakeSPI is licensed under a Creative Commons Attribution-Non Commercial 3.0 New Zealand License 2012. Visit the NIWA LakeSPI website.

LakeSPI information has been provided by NIWA.

Sites

Monitored sites on Te Whanga Lagoon

...retrieving sites.

No sites found.