Which human activity is most directly associated with pollution in the ocean?

Agricultural runoff is directly associated with ocean pollution because it involves the leaching of fertilizers, pesticides, and other chemicals from agricultural land into nearby waterways. When it rains, these substances can wash into rivers, streams, and eventually the ocean, leading to nutrient pollution, which causes harmful algal blooms. These blooms can deplete oxygen in the water, resulting in dead zones where aquatic life struggles to survive. The runoff contains not only nutrients like nitrogen and phosphorus but also pathogenic microorganisms and heavy metals, compounding the impact on marine ecosystems. This connection between agricultural practices and the degradation of ocean health underlines the critical role of land-based human activities in marine pollution.