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Water Quality

What water quality problems affect the Bay? Nitrogen and phosphorus pollution are the most serious problems facing the Bay. Too much nitrogen and phosphorus cause algae blooms that block sunlight to underwater grasses. When the blooms decompose, they create dead zones where dissolved oxygen levels are too low to sustain fish and shellfish. Excess sediment also degrades water quality. Poor water quality results in the loss of habitat for aquatic species throughout the Bay and its tidal and free flowing rivers. The Bay TMDL sets limits for these pollutants.

How do activities on land impact Chesapeake Bay water quality?  At its healthiest in the early 1600s, the Chesapeake watershed was mainly comprised of forested buffers, wetlands, and resources lands (open space and farmland) that absorbed and filtered nutrients. As development occurred throughout the watershed, farms, factories, cities, and suburbs have replaced natural wetland filters and forested buffer areas, resulting in the increased flow of nutrients into waterways.

How are the TMDL pollution limits set?  EPA utilized a modeling tool called the Bay Watershed Model to determine nitrogen, phosphorus, and sediment load caps for each state and the District of Columbia. These pollution limits are expressed as allocations by segment-shed (sub-basins of major rivers) and by the larger river basins. Within each basin, allocations are identified for the following source sectors: wastewater, onsite/septic, agriculture, urban stormwater, and forest.

Will the Bay TMDL have benefits for waterways throughout the watershed? The pollution controls employed to meet the TMDL will have significant benefits for water quality in the streams, creeks and rivers throughout the region, improving waterways that support local economies and livelihoods, provide for fishing, swimming, and boating opportunities, and often serve as sources of drinking water.