This document establishes Total Maximum Daily Loads (TMDLs) for nitrogen and phosphorus in the tidal stream segment of the Back River (basin number 02130901). The Back River drains into the Chesapeake Bay and is part of the Patapsco/Back River Tributary Strategy Basin. The tidal stream segment of the Back River (basin number 02130901) was first identified on the 1996 303(d) list submitted to EPA by the Maryland Department of the Environment (MDE) as being impaired by nutrients due to signs of eutrophication, expressed as high chlorophyll a levels. Eutrophication is the over-enrichment of aquatic systems by excessive inputs of nutrients (nitrogen and/or phosphorus). The nutrients act as a fertilizer leading to the excessive growth of aquatic plants. These plants eventually die and decompose, leading to bacterial consumption of dissolved oxygen (DO). For these reasons, this document proposes to establish TMDLs for the nutrients nitrogen and phosphorus in the Back River. The Back River was also identified on the 303(d) list as being impaired by bacteria (fecal coliform), toxics (PCBs), metals (Zinc) and suspended sediments. The impairments due to these contaminants have been or will be addressed in separate analyses by MDE. The water quality goal of these TMDLs is to reduce high chlorophyll a concentrations that reflect excessive algal blooms, and to maintain the dissolved oxygen criterion at a level whereby the designated uses for the Back River will be met. The TMDLs for the nutrients nitrogen and phosphorus were determined using a time-variable, three-dimensional water quality eutrophication model package, which includes the water quality model, Corps of Engineers- Water Quality-Integrated Compartment Model (CE-QUAL-ICM), a sediment process model, and the hydrodynamic model, Curvilinear Hydrodynamic in Three Dimensions (CH3D). Loading caps for total nitrogen and total phosphorus entering the Back River are established for low flow conditions and for annual average flow conditions.