Ammonia is a chemical of concern because elevated concentrations can cause serious harm to aquatic life in the Fox River and Bay of Green Bay.  High concentrations of ammonia are usually found in warm waters with low dissolved oxygen content and high alkalinity (pH).

The form of ammonia that is most lethal is unionized ammonia (NH3).  A concentration of 120 ug/L can cause acute toxicity or death to fish and invertebrates.  State water quality criteria for ammonia levels are based on both the pH and the temperature of the water.  Discharge limits for ammonia have been developed for both summer and winter conditions.  Maximum concentrations should not exceed 0.21mg/L for the Fox River and the AOC for the Bay of Green Bay.