Excess algal blooms in lakes, also known as eutrophication, occurs when there is an overabundance of nutrients such as nitrogen and phosphorus in the water. These nutrients can come from a variety of sources, including agricultural runoff, sewage discharge, and urban stormwater runoff. When there is an excess of nutrients in the water, it can lead to an increase in the growth of algae and other aquatic plants. As these plants die and decompose, the bacteria that break them down consume oxygen from the water. This can lead to a decrease in the amount of dissolved oxygen in the water, which can have negative effects on aquatic life. The chemical reactions associated with excess algal blooms involve the uptake of nutrients by the algae and their subsequent growth and reproduction. Algae use nitrogen and phosphorus as essential nutrients for photosynthesis and growth. As the algae grow and reproduce, they consume more and more of the available nutrients, which can lead to the depletion of these nutrients in the water. The negative effects of eutrophication on lakes can include a decrease in water clarity, an increase in the growth of harmful algal blooms, and a decrease in the amount of dissolved oxygen in the water. This can lead to the death of fish and other aquatic organisms, as well as the loss of recreational opportunities such as swimming and fishing. In addition, the presence of harmful algal blooms can pose a risk to human health, as some species of algae can produce toxins that are harmful to humans and animals.