The Federal Clean Water Act requires that states and tribes restore and maintain the chemical, physical, and biological integrity of the nations waters. States and tribes, pursuant to Section 303 of the Clean Water Act, are to adopt water quality standards necessary to protect fish, shellfish, and wildlife while providing for recreation in and on the nations waters whenever possible. Section 303(d) of the Clean Water Act establishes requirements for states and tribes to identify and prioritize water bodies that are water quality limited (i.e., water bodies that do not meet water quality standards). States and tribes must periodically publish a priority list (a SC303(d) list) of impaired waters. Currently this list must be published every two years. For waters identified on this list, states and tribes must develop a total maximum daily load for the pollutants, set at a level to achieve water quality standards. This document addresses one water body in the Lower Payette River Subbasin that has been placed on Idahos current SC303(d) list. For more information about this watershed and the subbasin see the Lower Payette River Subbasin Assessment and Total Maximum Daily Loads. The first part of this document, the Subbasin Assessment (SBA), is an important first step in the TMDL. The starting point for this assessment was Idahos 1998 SC303(d) list of water quality limited water bodies. Big Willow Creek, from the headwaters to the mouth, is on this list. The SBA examines the current status of SC303(d) listed waters and uses available data to define the extent of impairment and identify potential causes of water quality impairment throughout the subbasin. The TMDL analysis quantifies pollutant sources and allocates responsibility for load reductions needed to return listed waters to a condition that meets Idaho water quality standards. This TMDL analysis has been developed to comply with Idahos Total Maximum Daily Loads schedule. During the development of this TMDL, Idaho published a new list of impaired waters (2002) by Assessment Units (AUs), designated by stream order (Strahler, 1957), and adopted revised water quality standards (2007). The 2002 list was approved by EPA in 2005 and lists Big Willow Creek 1st and 2nd order segments (ID17050122SW017-02), 4th order segments (ID17050122SW017-04), and 6th order segments (ID17050122SW017-06) as impaired for unknown pollutants. There are no identified fifth order stream segments in the Big Willow Creek subbasin, and no corresponding ID number with an 05 suffix. Big Willow Creek from headwaters to mouth was listed as impaired for temperature by EPA and included in Idahos TMDL schedule.