Executive Summary
This report provides a snapshot of current lake water quality and lake water quality monitoring in New Zealand. It reports on what monitoring is being done by councils and provides a national summary of these monitoring results. The report focuses on collating recently published information rather than on analysing actual water quality data. This means that some caution is needed when comparing water quality state and trends between different lakes because data was analysed over different time periods.
This survey identifies that 153 New Zealand lakes are being monitored by 13 councils for trophic status, ecological condition or cyanobacteria through bathing beach monitoring programmes. Trophic status is being assessed in 119 lakes and ecological condition is being assessed using LakeSPI (submerged plant indicators) in 86 lakes. The number of lakes monitored by regional councils is expanding. Prior to 2000, about 87 lakes were being monitored (68 for trophic status). Since then, lake water quality monitoring has been initiated in Northland, Southland and the Chatham Islands, will be initiated in Hawke's Bay this year and has been expanded in other regions (eg, Otago).
LakeSPI monitoring provides valuable information on lake ecological condition but its use is currently restricted to three councils in the North Island. This means that no LakeSPI information is being reported for the South Island and for some lake types. It is likely several more councils will adopt LakeSPI monitoring in the near future (eg, Hawke's Bay Regional Council).
Lake trophic state is reported for 134 lakes using current and past monitoring programmes. Slightly over half the lakes monitored are eutrophic or worse. This not only reflects pressures on the lakes but also the tendency for shallower lakes to be more eutrophic.
Information on trends in trophic state is available for 70 lakes and shows that more lakes are improving (33 percent) compared to those with declining quality (19 percent). This is mostly due to improved water quality in the already pristine Canterbury high-country lakes. Trends in ecological condition were available for 46 lakes and are not so positive. Half the lakes show a decline in condition and only 22 percent show an improvement. This can be attributed to pressures such as invasive plants, exotic fish, sediment loads and nutrients.
Several gaps in our ability to report lake water quality at a national level were identified. These gaps relate to the extent to which indicators are used, the extent to which the monitoring network is representative of New Zealand lakes, and to ensuring appropriate management objectives against which to report. To improve our ability to report on national lake water quality it would be helpful to have appropriate targets or reference conditions for different types of lakes. A lake classification system is currently being developed by NIWA and the Department of Conservation which may improve our framework for reporting on lake water quality. Recommendations are made for further work.
