Ammonium is a polyatomic ion with a chemical formula of NH4+, that is formed by adding an H+ ion to ammonia (NH3). Ammonia enters the water from aquatic animals’ wastes, decaying plants, food, and is also actively transported from fish gills. It is then converted to ammonium in water by bacteria. Ammonium interferes with sodium-potassium ATPase channels in nerves, meaning it is toxic, killing the fish and affecting the development of tissues in the liver, gills, and kidneys. In addition, it damages plant cells, causing the leaf edges of the plant to curl, and eventually die. Moreover, it slows down the growth of the roots of plants and the growth rates of the fish. Some organisms, such as mussels, find it difficult to remove ammonium from their system. Therefore, it is converted in the urea cycle to urea, which is less toxic and more efficiently stored.