Lake Okaro

Okaro is a small lake with very high productivity and is classed as super-trophic. It is subject to frequent and severe blooms of cyanobacteria (blue-green algae) during summer. It has been the focus of an extensive water quality management programme, including land-based interventions such as agricultural detention bunds, wetlands and in-lake remediation (flocculation and sediment capping).

Lake Okaro is surrounded by pasture and is fed by several small streams. It has an outlet stream (Haumi Stream) to the east, which drains to Lake Rotomāhana. The lake’s average depth is 12m and sampling occurs at the maximum depth of 18m. Poor water clarity in Lake Okaro restricts aquatic plant growth. While the lake contains few invasive weed species, the native condition index is the lowest of the 12 lakes and subsequently the LakeSPI (submerged plant indicators) score is one of the lowest recorded. Restoration initiatives for Lake Okaro have focused on reducing the external and internal nutrient loads. A 2.3ha wetland was completed in 2007 to intercept dissolved nutrients through incorporation into organic matter within the wetland, and through denitrification of nitrate to nitrogen gas. A detainment bund upstream of the wetland was completed in 2014 to balance peak flows and settle out particulate matter. Other key actions that are being or will be implemented include full riparian protection, allophane treatment of the main inflow to remove phosphorus, storm water detention on farmland and ongoing monitoring.

Lake Summary

Lake size

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Geomorphic type

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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 Lake Okaro

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.

No data available.

TLI history for Lake Okaro 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.