Excess nitrogen can lead to eutrophication of water bodies by promoting the growth of algae and other aquatic plants. When these plants die, they sink to the bottom of the water body and decompose. This decomposition process consumes oxygen, leading to a decrease in the oxygen levels in the water. As oxygen levels decrease, fish and other aquatic animals may die or be forced to leave the area in search of more suitable habitats. Additionally, the decomposition process releases nutrients such as phosphorus and nitrogen back into the water, further promoting the growth of algae and other aquatic plants. This can create a cycle of eutrophication, where the growth and death of aquatic organisms leads to a decline in water quality and the loss of aquatic habitats.