When nutrient levels rise above natural levels for a body of…

When nutrient levels rise above natural levels for a body of water, an event called , it causes an algae bloom. The algae blocks , which kills some of the plants and algae at the bottom of the stream. At night, the algae stop doing photosynthesis and start to reduce the in the water, which stresses fish and other aquatic organisms. When the dead plants and algae get broken down by , the factor from the previous sentence becomes even more depleted, which may kill animals living in the water. With more dead material in the water, the cycle may continue until the water is unlivable.