The Nitrogen Indicator (official name: Indicator of the Risk of Water Contamination by Nitrogen) evaluates the risk of water contamination by nitrogen across agricultural areas in Canada. This indicator uses the Residual Soil Nitrogen Indicator, which calculates the amount of nitrogen left in the soil after harvest, as well as subsequent climatic factors to determine the risk of nitrogen reaching surface and ground water. It is important to note that the indicator examines risk of nitrate leaching — that is soluble nitrogen that has passed through the soil profile into ground water or into tile drainage water — rather than losses of nitrogen in surface runoff, which are considered to be minor. The indicator has tracked nitrogen risk associated with Canadian agricultural activities from 1981 to 2021.