Waikato River - wastewater discharges

Geothermal fluids from geothermal power stations are a major source of arsenic, boron and other geothermal chemicals found in the Waikato River. Since the Wairakei Power Station was built in the late 1950s, the amount of arsenic in the Waikato River has more than doubled.

Arsenic levels in the river now exceed drinking water standards. This means a high level of water treatment is needed for drinking water supply. To reduce this effect on the river the Ohaaki geothermal field re-injects waste geothermal fluid back into the ground. This is also beneficial for the geothermal systems themselves. 

Wastewater from the Kinleith Mill is a major source of dissolved colour or dark tea-coloured staining in the upper river. In 1991 when a new treatment process was introduced, the amount of dissolved colour in the mill’s waste water halved, causing levels in the river to fall. As a result, the Waikato River is now a brighter green colour than it was during the 1980s.

A recent study of bacteria levels (an indicator of health risk) in the lower river showed that discharges of wastewater are not a major source of bacteria to the river as a whole. 

The three major point sources of bacteria to the river between the Narrows and Huntly (Hamilton sewage, Ngāruawāhia sewage and a meat-works) account for only five per cent of the total bacteria levels found in the lower river. This indicates that most of the bacteria found in the river must come from non-point sources such as rural runoff.

In the upper river, since the sewage discharge from Taupō township stopped in 1995, bacteria have reduced to safe swimming levels downstream, nutrient levels have dropped and nuisance algae no longer spoils the way the river looks. Most people would be surprised but pleased to know that Huka Falls, the image of unspoilt New Zealand, is now much cleaner than it was in the 1980s!