Total Maximum Daily Load

A total maximum daily load (TMDL) specifies the maximum amount of a pollutant load that a water body can receive and still meet water quality standards. A TMDL allocates pollutant loadings among point and nonpoint sources, background levels, reserves for future growth, and a margin of safety. Point sources are typically defined as those sources that enter surface waters through a pipe or defined conveyance system (i.e., municipal and industrial stormwater and/or wastewater). Waste load allocations (WLAs) are provided in the TMDL for point sources. Nonpoint sources are typically defined as those sources that enter surface waters through more diffuse and dispersed overland flow (e.g., surface runoff from agricultural and forested lands). Load allocations (LAs) are provided in the TMDL for nonpoint sources. 

On September 21, 2006, DEQ finalized the first version of the TMDL for the Willamette Basin. This document has been revised and updated multiple times with the most recent version being from May of 2025. The TMDL addressed water quality impairment of the Middle Willamette River and its tributaries and included previously-approved TMDLs by reference. The Willamette Basin TMDL addressed bacteria, mercury, and temperature, and included WLAs and LAs specific to DMAs.