Fact Sheet 

 Chesapeake Bay 

 Total Maximum Daily Load (TMDL) 

Driving Actions to Clean Local Waters and the Chesapeake Bay 

On Dec. 29, 2010, the U.S. Environmental Protection Agency established the Chesapeake 

Bay Total Maximum Daily Load (TMDL), a historic and comprehensive “pollution diet” 

with rigorous accountability measures to initiate sweeping actions to restore clean water 

in the Chesapeake Bay and the region’s streams, creeks and rivers. 

Despite extensive restoration efforts during the past 25 years, the TMDL was prompted 

by insufficient progress and continued poor water quality in the Chesapeake Bay and its 

tidal tributaries. The TMDL is required under the federal Clean Water Act and responds 

to consent decrees in Virginia and the District of Columbia from the late 1990s. It is also 

a keystone commitment of a federal strategy to meet President Barack Obama’s 

Executive Order to restore and protect the Bay. 

The TMDL – the largest ever developed by EPA, 

encompassing a 64,000-square-mile watershed – identifies 

the necessary pollution reductions from major sources of 

nitrogen, phosphorus and sediment across the District of 

Columbia and large sections of Delaware, Maryland, New 

York, Pennsylvania, Virginia and West Virginia, and sets 

pollution limits necessary to meet water quality standards 

in the Bay and its tidal rivers. 

Specifically, the TMDL sets Bay watershed limits of 185.9 

million pounds of nitrogen, 12.5 million pounds of 

phosphorus and 6.45 billion pounds of sediment per year – 

a 25 percent reduction in nitrogen, 24 percent reduction in 

phosphorus and 20 percent reduction in sediment. 

The pollution limits are further divided by jurisdiction and major river basin based on 

state-of-the-art modeling tools, extensive monitoring data, peer-reviewed science and 

close interaction with jurisdiction partners. The TMDL is designed to ensure that all 

pollution control measures needed to fully restore the Bay and its tidal rivers are in place 

by 2025, with at least 60 percent of the actions completed by 2017. 

The final TMDL is shaped by an extensive two-year public involvement effort and, in 

large part, by final Phase I Watershed Implementation Plans (WIPs) developed by the six 

Bay states and the District of Columbia, which detail how and when the jurisdictions will 

meet pollution allocations. 

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In addition, the TMDL includes targeted “backstop allocations” for the few areas where 

the WIPs did not meet the allocations or EPA’s expectations of reasonable assurance that 

those allocations would be met, and a plan for enhanced oversight and contingency 

actions to ensure progress. 

Also, EPA has committed to reducing air deposition of nitrogen to the tidal waters of the 

Bay from 17.9 to 15.7 million pounds per year through federal air regulations during the 

coming years. 

The Chesapeake Bay TMDL is unique because of the extensive measures EPA and the 

jurisdictions have adopted to ensure accountability for reducing pollution and meeting 

deadlines for progress. The accountability framework includes the WIPs, two-year 

milestones, EPA’s tracking and assessment of restoration progress and, as necessary, 

specific federal actions if the jurisdictions do not meet their commitments. 

Addressing the Challenges 

A TMDL is the calculation of the maximum amount of pollution a body of water can 

receive and still meet state water quality standards designed to ensure waterways meet a 

national primary goal of being swimmable and fishable. Monitoring data continues to 

show that the Bay has poor water quality, degraded habitats and low populations of many 

species of fish and shellfish. The Bay and its rivers are overweight with nitrogen, 

phosphorus and sediment from agricultural operations, urban and suburban runoff, 

wastewater, airborne contaminants and other sources. The excess nutrients and sediment 

lead to murky water and algae blooms, which block sunlight from reaching and 

sustaining underwater Bay grasses, and create low levels of oxygen for aquatic life, such 

as fish, crabs and oysters. 

The Bay TMDL – actually a combination of 92 smaller TMDLs for individual 

Chesapeake Bay tidal segments – includes pollution limits sufficient to meet state water 

quality standards for dissolved oxygen, water clarity, underwater Bay grasses, and 

chlorophyll a, an indicator of algae levels. 

Actions under the TMDL will also have significant benefits far beyond the Chesapeake 

itself, helping to clean rivers and other waterways that support local economies and 

recreational pursuits like fishing and swimming, and serve as drinking water sources. 

In 2011, while the jurisdictions continue to implement their WIPs, they will begin 

development of Phase II Watershed Implementation Plans, designed to more closely 

engage local governments, watershed organizations, conservation districts, citizens and 

other key stakeholders in reducing water pollution. The Phase II WIPs are expected to 

provide local area targets for implementation on a smaller scale. Phase III WIPs in 2017 

are expected to be designed to provide additional detail of restoration actions beyond 

2017 and to ensure that the 2025 goals are met. 

For Further Information, View: http://www.epa.gov/chesapeakebaytmdl

(Last Updated: 12/29/10)