As part of an overall ecosystem assessment of lower Karori Reservoir Sabctuary, Wellington, a number of variables are being monitored routinely, including temperature, nutrients, and phytoplankton and zooplankton populations. Ammonium (NH₄) tends to be the dominant species of inorganic nitrogen most of the time except in late winter when nitrate (NO₃) becomes dominant. Total nitrogen concentrations place Karori Sancturay in a mesotrophic to eutrophic category.