What affect does excess nitrogen have on organisms in a pond or lake ecosystem?

Excess nitrogen in a pond or lake ecosystem can lead to nutrient pollution, resulting in algal blooms that deplete oxygen levels in the water. This hypoxia can harm or kill aquatic organisms, such as fish and invertebrates, disrupting the food web and overall biodiversity. Additionally, the excess algae can block sunlight, hindering the growth of submerged aquatic plants, further destabilizing the ecosystem. Ultimately, these changes can lead to a decline in water quality and the health of the ecosystem.