Why is excessive algae growth negative for a lagoon?

Excessive algae growth in a lagoon can be detrimental primarily because it blocks sunlight and decreases dissolved oxygen (DO) levels. Algae require light for photosynthesis, and when they proliferate excessively, they can create a dense cover on the water surface. This cover reduces the penetration of sunlight into the water below, which affects not only the algae themselves but also other aquatic plants that rely on light for growth.

Moreover, when the algae die off, their decomposition consumes a significant amount of dissolved oxygen in the water, leading to lower oxygen levels. This decline in DO levels can harm or even kill fish and other aquatic organisms that depend on oxygen for survival. Maintaining appropriate oxygen levels is crucial for the overall health of the lagoon's ecosystem, making this an important consideration in wastewater treatment processes involving lagoons.