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How can algal blooms lower oxygen levels in water?

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“mermaid's wine glass” algae — Algae The macroscopic genus of algae known as *Acetabularia* is commonly called “mermaid's wine glass” because of the distinctive umbrella-like shape of the tips of its stalks.

Algal blooms, which are dense populations of microscopic photosynthetic organisms, can significantly lower oxygen levels in water through a process often linked to eutrophication.12

When an abundance of nutrients—such as nitrogen and phosphorus from fertilizers or waste—enters a body of water, it triggers rapid, excessive growth of phytoplankton and other algae. The oxygen depletion occurs primarily after these massive populations reach their peak and begin to die. As the large masses of algae die and sink, they are broken down by bacteria and other decomposers. This decomposition process consumes vast amounts of dissolved oxygen from the water.132

The resulting low-oxygen environment, often called a "dead zone," can lead to the suffocation and death of aquatic life, including fish, shrimp, and crabs. Additionally, while algae produce oxygen through photosynthesis during the day, the respiration of such a dense population can also contribute to oxygen decline, particularly in still or warm conditions.1345