Water quality in Kapiti Marine Reserve

Introduction

How good is the water quality in Kapiti Marine Reserve and how is it changing?

Marine reserve

The water in Kapiti Marine Reserve is influenced by the strong currents that move through the area and by the rivers and streams that enter it.

Status: good

Greater Wellington Regional Council’s recreational water quality monitoring programme rates its sampling sites at Ara Kuaka carpark, Waikanae Beach (just north of the marine reserve) as ‘B: good, low risk of illness’ for swimming and other recreational activities.

This rating is based on the number of Enterococci bacteria (which can cause serious health problems) per 100 mL of water in weekly monitoring from the start of December until the end of March each year. Levels of Enterococci are known to rise during and after periods of heavy rain.

Trend: stable

Based on the recreational water quality monitoring, the water quality at the Ara Kuaka carpark site has been below the alert level for the last 5 years, apart from one occasion. 

View the monitoring data.
Read more about the monitoring programme 

Kapiti Island

Because Kapiti Island is a nature reserve, streams from the island that enter the marine reserve are likely to contain low levels of pollutants. No regular monitoring of these streams is carried out.

Waikanae River

The Waikanae River begins in the foothills of the Tararua Ranges and enters the marine reserve on its eastern boundary. Its waters can become contaminated with sediment after heavy rain, mainly from forestry and urban development in the catchment. Contaminated stormwater from local roads, particularly the State Highway 1 expressway, is designed to travel through treatment ponds and wetlands before it enters the river. Treated wastewater also flows into the river from the Paraparaumu Treatment Plant via the Mazengarb Drain (a tributary of the Waikanae River).

Greater Wellington Regional Council monitors the water quality monthly at two sites on the Waikanae River. In 2016/17 these sites had good to excellent water quality. 

Waikanae Estuary

Waikanae Estuary is one of Greater Wellington Regional Council’s priority coastal monitoring sites. Annual monitoring of the estuary (sediment, algae and invertebrate community) from 2008 to 2010 and in 2015 showed that fine sediment, or mud, was an issue in the estuary from time to time. 

Since 2010, the rate of sedimentation over concrete plates buried in the estuary has been measured annually. Mapping of the habitats and substrate (mud and sand) is also carried out every 5 years. The mean sedimentation rate was 18.4 mm per year for the last 5 years – a result that places the estuary at high risk of having poor water clarity and muddy, oxygen-depleted sediments. 

Metal contaminants and nutrients occur in very low concentrations. Seagrass has been completely lost from the estuary and only small areas of saltmarsh remain. The invertebrate communities in the estuary are very variable because the proportions of mud and sand fluctuate. This variability is typical of estuaries like Waikanae. 

Reports

See also research and monitoring.

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