Ammonia (chemical formula NH3) is a gas and a common nitrogen-based pollutant that at high concentrations and under certain temperature and pH conditions is toxic to many species, particularly fish and invertebrates. Direct discharges to waterways of animal or domestic effluent, industrial discharges, runoff and decaying organic material can contribute to high levels of ammonia. Ammonia converts to ammonium (NH4) when it is dissolved in water and can be converted to nitrite (NO2) and nitrate (NO3) by bacteria.

View a factsheet on Nitrogen.