This document, upon approval by U.S. Environmental Protection Agency, establishes Total Maximum Daily Loads (TMDLs) for nitrogen and phosphorus in the Upper Chester River (basin number 02-13-05-10) and the Middle Chester River (basin number 02-13-05-09). The Upper Chester River and Middle Chester River are part of the Upper Eastern Shore Tributary Strategy Basin. These river segments are impaired by the nutrients nitrogen and phosphorus, which cause excessive algal blooms accompanied by reduced concentrations of dissolved oxygen. The Upper Chester River, located within Kent and Queen Annes Counties, was first identified on the States 1996 303(d) list as impaired by nutrients, sediments, and bacteria, with listings added in 2002 for evidence of biological impacts, and in 2004 for methylmercury in fish tissue in one of the basins impoundments (Millington Wildlife Management Ponds). The sediment, bacteria, biological, and methylmercury in fish tissue impairments will be addressed separately. The Middle Chester River, located within Kent and Queen Annes Counties, was first identified on the States 1996 303(d) list as impaired by nutrients, sediments, and bacteria. In 2002, polychlorinated biphenyls (PCBs) in fish tissue and evidence of biological impacts were added, with additional subbasins listed as impaired by evidence of biological impacts in 2004. TMDLs to address the nutrient and sediment listings of Urieville Community Lake, an impoundment within the Middle Chester Watershed, were submitted and approved in 1999; the sediment, bacteria, PCBs in fish tissue and biological impacts will be addressed separately. The water quality goal of these TMDLs is to reduce high chlorophyll a (Chla) concentrations (a surrogate for algal blooms) and to maintain dissolved oxygen (DO) at a level supportive of the designated uses for the Upper and Middle Chester Rivers. The TMDLs for the nutrients nitrogen and phosphorus were determined using a time- variable, three-dimensional water quality eutrophication model package that includes a water quality model, Corps of Engineers-Water Quality-Integrated Compartment Model (CE-QUAL-ICM); and a hydrodynamic model, Curvilinear Hydrodynamic in Three Dimensions (CH3D). Loading caps for total nitrogen and total phosphorus entering the Upper and Middle Chester Rivers are established for the growing season (critical conditions) and for average annual flow conditions. The growing season TMDLs apply from May 1 through October 31. For the Upper Chester River, the growing season TMDL for nitrogen is 246,717 lbs/growing season, and the growing season TMDL for phosphorus is 8,573 lbs/growing season. The allowable loads have been allocated between point and nonpoint sources. The Upper Chester River nonpoint sources are allocated 224,377 lbs/growing season of total nitrogen, and 6,872 lbs/growing season of total phosphorus. The Upper Chester River point sources are allocated 11,913 lbs/growing season of nitrogen, and 1,366 lbs/growing season of phosphorus. An explicit margin of safety makes up the remainder of the nitrogen and phosphorus allocations.