Water quality in the Waikato River is much better than it was in the 1950s. Urban waste water treatment has improved considerably. Over the past ten years, however, levels of nitrogen and phosphorus in the river have risen, probably as a result of land use changes over recent decades.
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Pollution of the past
The Waikato River's water quality has improved a great deal from what it once was. It is the country's longest river - and 40 years ago, one of the dirtiest. Today it is not pristine but it's now much cleaner than in 1950s and 60s. A description from the Pollution Advisory Council in 1956 sums up the way the river was once used:
"the daily flow of sewage effluent and trade wastes from Hamilton City is three million gallons… in effect, partly digested sludge and raw sewage is being disposed of into the Waikato River".
Water quality records from upstream of Hamilton City date from 1949. They show that levels of sewage-related contaminants have stayed roughly the same. However, as the city grew, measurements taken downstream of Hamilton City revealed contaminants increased 10-fold between the 1950s and early 1970s.
In those days, Hamilton's wastewater was discharged to the river after holding in 14 large septic tanks. In addition, the tanks themselves were emptied into the river up to three times each year. The river also handled sewage from other towns, along with effluent from the Horotiu freezing works, Kinleith paper mill, power projects and dairy farms.
The road to recovery
Improvements to urban waste water treatment
Since the 1970s, considerable work has been done to improve the quality of effluent from industrial and urban sources. The 1970s saw major improvements to urban wastewater treatment. The longest water quality record for the Waikato River (at Mercer) shows that this was when river water quality began to improve.
The high levels of contaminants evident in the early 1970s fell to levels ten times lower during the late 1970s and early 1980s.
Recent changes in water quality
Limited monthly monitoring of water quality in the Waikato River began in 1980, with a more comprehensive programme beginning in 1987. We now sample at 10 sites along its length (view a map of monitoring sites or find out more about how we measure water quality). Analysis of this record indicates how water quality has changed (Table 1).
Table 1 shows the changes in several water quality measures during the 20-year period between 1989 and 2008. Overall, 25 percent of water quality measures improved at individual sites, and 22 percent deteriorated.
Biochemical oxygen demand – a measure of pollutants that consume oxygen in the water as they break down – improved along the entire length of the river. These improvements are probably at least partly due to changes in the management of sewage and industrial wastewaters.
At the same time, levels of both total phosphorus and nitrate increased at several sites along the river, probably as a result of land use changes over recent decades. Pressures from wastewaters have generally decreased over the past 20 years, but farming has continued to intensify.
Table 1: Water quality trends in the Waikato River between 1989 and 2008 (based on methods in Environment Waikato Technical Report 2008/33)
The recent increases in levels of phosphorus and nitrogen are of concern. As the region continues to grow and develop - putting pressure on the river's catchment - careful management is needed to maintain and improve the quality of the Waikato River.
What can you do to help protect the Waikato River?
- Don’t tip hazardous substances (such as paint washings or used oil) into stormwater drains.
- Adopt careful land management practices to minimise contaminated runoff from your property. Read about our Care programmes and services for farmers.
- Fence riverbanks to keep stock out and prevent stock damage.
- Work with Environment Waikato to obtain a resource consent if you want to discharge waste water to the River. Check out our consents information here.
- Don’t waste water – use it more efficiently and effectively.