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In 2010, the U.S. Environmental Protection Agency established the Chesapeake Bay Total Maximum Daily Load (TMDL)—the largest cleanup plan to date designed to restore clean water in the bay watershed. The TMDL established limits on nitrogen, phosphorus and sediment and set compliance milestones in order to meet water quality standards for dissolved oxygen, water clarity, bay grasses, and chlorophyll-a. Under the TMDL, pollution control measures must be in place to meet reduction targets by 2025 with at least a 60 percent (of 2009 levels) reduction by 2017. Each of the six bay states, including Pennsylvania, and the District of Columbia developed watershed implementation plans (WIPs) detailing how and when they would meet their pollution allocations.

The Chesapeake Bay Program, a regional partnership that includes the EPA and the other TMDL jurisdictions, including Pennsylvania, has determined that agriculture is the largest source of nutrient (nitrogen and phosphorus) and sediment contamination entering the bay. Nutrient runoff from agricultural operations enters streams that flow into the bay, causing algal blooms and the resulting low-oxygen “dead zones” that are harmful to aquatic life.