How do dead zones occur?

Dead zones occur in aquatic environments when excessive nutrients, particularly nitrogen and phosphorus from agricultural runoff and wastewater, lead to algal blooms. When these blooms die and decompose, the decomposition process consumes dissolved oxygen in the water, creating low-oxygen conditions. This hypoxia can be detrimental to marine life, leading to fish kills and loss of biodiversity. As a result, areas become "dead zones" where most marine organisms cannot survive.