Phosphorus

Phosphorus is a type of nutrient contributing to the Bay's poor water quality. While phosphorus is vital to plant life, human activities—from applying fertilizers to using household cleaners—contribute more phosphorus than the Bay's waters can handle. Elevated phosphorus levels cause more algae to grow, blocking out sunlight and reducing oxygen for fish, blue crabs and other Bay life.

Where does phosphorus come from?

• Non-agricultural fertilizers and eroding sediment from stream banks in urban and suburban areas (30 percent). Phosphorus often attaches to soil and sediment particles on land, entering the Bay many years later when stream banks erode.
• Manure from agricultural lands (27 percent)
• Treated wastewater released from municipal and industrial wastewater facilities (22 percent)
• Chemical fertilizers from agricultural lands (18 percent)
• Natural sources, including forests and wildlife (3 percent)

How is excess phosphorus a pressure on the Bay?

Excess phosphorus fuels the growth of algae, creating dense algae blooms that rob the Bay's aquatic life of sunlight and dissolved oxygen.

• Algae blooms on the surface of the water block the sun's rays from reaching underwater bay grasses growing at the bottom . Algae can also grow directly on the grasses' leaves, further reducing the amount of sunlight they receive. Without sunlight, bay grasses cannot grow and provide critical food and habitat for blue crabs, waterfowl and juvenile fish.

• “Leftover” algae that are not consumed by the Bay's algae-eating organisms eventually die and sink to the bottom. There, they are decomposed by bacteria in a process that leaves bottom waters with little or no dissolved oxygen for crabs, oysters and other bottom-dwelling species. Just like humans and animals on earth, all aquatic species need oxygen to survive.