The primary cause of eutrophication in coastal waters is nutrient runoff, particularly nitrogen and phosphorus from agriculture and urban areas. These nutrients enter water bodies, leading to excessive growth of algae (algal blooms). As the algae die and decompose, oxygen levels deplete, resulting in hypoxia or "dead zones," where aquatic life cannot survive. Eutrophication disrupts marine ecosystems, reduces biodiversity, and negatively impacts fisheries and recreation. Addressing nutrient loading through better management practices is essential to combat eutrophication and restore healthy coastal environments.