State of the Wetlands

Lake Wairarapa view from Western Lake Road looking north

Lake Wairarapa is among New Zealand’s 10 dirtiest lakes. It is shallow, being only up to two and a half metres deep. Because it carries a high sedimentation load which is stirred up by the winds that sweep across the water, the lake appears mostly muddy grey in colour. The lake also has high levels of nutrients and lots of algal growth.

This is the legacy of being the receiving environment for sediment washing off Wairarapa’s erodible hills, the towns’ sewage systems, dairy factories and other industrial waste. That was until the 1970’s after which the Ruamahanga River was diverted past Lake Wairarapa and directly into Lake Onoke.

Changes in environmental standards means far less waste is put into our rivers and streams. However, Lake Wairarapa can still get water containing treated municipal waste water from Featherston and agricultural run-off.

How are the wetlands doing?

Several large drainage schemes on the eastern lake shore direct nutrient rich water, drained from pasture, into adjacent wetlands and on into the lake. Monitoring shows that some edge wetlands are in a poorer state than the lake, with higher concentrations of nutrients and algae. This means the wetlands are probably overloaded and not able to filter water as well as they normally would. 

Why does this matter?

The presence of extra nutrients and sediment are threats to the natural balances in a wetland ecosystem. Much of the native biodiversity won’t thrive in an environment with poor water quality and with competing weeds. An example of this is the state of five species of whitebait fish species – inanga, koaro, short-jawed kokopu, banded kokopu and giant kokopu. They are found in much reduced numbers than would be expected if the Moana was in better health.