How do sewage and agricultural runoff pollute Atlantic coastal waters?

Sewage and agricultural runoff significantly degrade Atlantic coastal waters primarily through a process known as cultural eutrophication.1

When these substances enter coastal ecosystems, they introduce excess nutrients—specifically nitrogen and phosphorus—that trigger the rapid, excessive growth of algae and other microscopic organisms. This phenomenon, often called a water bloom, has several destructive consequences:12

• Oxygen Depletion: As these massive algal populations die and decompose, the process consumes vast amounts of dissolved oxygen. This creates hypoxia, or "dead zones," where oxygen levels become too low to support marine life, leading to the suffocation of fish, crabs, and other bottom-dwelling organisms.231
• Ecosystem Imbalance: The nutrient overload shifts the balance of marine habitats, often favoring algae over native species like corals, which can lead to widespread disease outbreaks and a decline in biodiversity.3
• Toxic Effects: Nutrient loading can trigger toxic blooms, such as red tides, which may poison wildlife and pose health risks to humans.13

These pollutants reach the Atlantic via rivers and estuaries, which act as conduits for land-based waste, including untreated sewage and fertilizer runoff from croplands and animal feedlots.123