The findings of the Organisation for Economic Co‐operation and Development Cooperative Programme on Eutrophication are largely inapplicable to lakes in New Zealand. This is because the relative distributions of nutrient nitrogen and phosphorus in New Zealand lakes and those of the OECD study are very different. The limnological feature central to the OECD findings is that phosphorus is the nutrient limiting algal growth, nutrient nitrogen usually being massively in excess of algal requirements. This is not true in New Zealand, where nitrogenous material in fresh waters is very much less abundant. In many lakes here the relative availability of nitrogen to phosphorus approximates that required for balanced algal growth, and in some, shortage of nitrogen limits growth. Water managers aiming to control eutrophication in New Zealand lakes are advised to use the OECD predictive equations with the utmost caution.