Ammonia

Nitrogen occurs in natural waters as nitrate (NO₃), nitrite (NO₂), ammonia (NH₃) and organically bound nitrogen. As aquatic plants and animals die, bacteria break down huge protein molecules holding nitrogen into ammonia. Sewage is the main source of ammonia added by humans to rivers. The ammonia arises mostly from the hydrolysis of urea in urine, but further ammonia is produced through the decomposition of other nitrogenous materials in sewage. Within a flowing stream, the presence of ammonia in high concentrations indicates recent pollution. Excessive amounts can cause a reduction in salmon hatching success and a reduction in growth rate among other things. The criterion for ammonia is dependent on other factors in the stream - such as pH and Temperature.