sentences:  Nitrifying bacteria thrive in lakes and rivers streams with high inputs and outputs of sewage and wastewater and freshwater because of the high ammonia content.Nitrification in nature is a two-step oxidation process of ammonium (NH4+) or ammonia (NH3) to nitrate (NO3−) catalyzed by two ubiquitous bacterial groups.The first reaction is oxidation of ammonium to nitrite by ammonia oxidizing bacteria (AOB) represented by the "Nitrosomonas" genus.