I'll assume this is to do with bodies of water and not the body.
Nutrient pollution is where there are too many nutrients, such as nitrogen and phosphorus, in bodies of water. These nutrients can act like fertilizer, causing excessive growth of algae.
Severe algal growth blocks light that is needed for plants, such as seagrasses, to grow.
When the algae and seagrass die, they decay. In the process of decay, the oxygen in the water is used up and this leads to low levels of dissolved oxygen in the water. This, in turn, can kill fish, crabs, oysters, and other aquatic animals.
