Lake water quality in New Zealand 2010: Status and trends

The report provides a national picture of current status (2005–2009) and trends in water quality of New Zealand lakes. It uses Trophic Level Index (TLI) and LakeSPI (submerged plant indicators) to provide a picture of nutrient levels and overall ecological condition, and discusses the results in the context of different lake types and land uses. In addition, a comparison of New Zealand lake water quality with a subset of lakes in Europe, USA and Canada is made.

Key findings

• Of the 4000 lakes in New Zealand over 1 hectare in size, 43 per cent are likely to have very good or excellent water quality (very low levels of nutrients), and 32 per cent are likely to have poor or very poor water quality (are nutrient enriched).
• The lakes with the poorest water quality and ecological condition tend to be surrounded by pastoral land cover.
• Between 2005 and 2009, 12 per cent of the 68 lakes assessed showed an improvement in water quality and 28 per cent deteriorated.
• The decline was most marked in lakes with predominantly native catchment cover (40 percent of lakes with native cover declined, compared with 25 per cent of lakes with pastoral cover).