The Big River Total Maximum Daily Load (TMDL) for Sediment is being established in accordance with Section 303(d) of the Clean Water Act, because the State of California has determined that the water quality standards for the Big River are exceeded due to sediment. In accordance with Section 303(d), the State of California periodically identifies those waters that are not meeting water quality standards. In its latest Section 303(d) list, adopted through Resolution 98-45 on 23 April 1998, the North Coast Regional Water Quality Control Board (NCRWQCB) identified the Big River as impaired due to sediment. In accordance with a consent decree (Pacific Coast Federation of Fishermens Associations, et al. v. Marcus, No. 95-4474 MHP, 11 March 1997), 2001 is the deadline for establishment of this TMDL. Because the State of California will not complete adoption of a TMDL for the Big River by this deadline, EPA is establishing this TMDL, with assistance from NCRWQCB staff. The primary adverse impacts associated with excessive sediment in the Big River pertain to the anadromous salmonid fishery. The water quality conditions do not adequately support several anadromous salmonid species present in the Big River and its tributaries, which has contributed to severe population declines. The populations of coho salmon (Oncorhynchus kisutch), chinook salmon (O. tshawytscha), and steelhead trout (O. mykiss) in this watershed are all listed as threatened under the federal Endangered Species Act. The purpose of the Big River TMDL is to identify the total load of sediment that can be delivered to the Big River and its tributaries without causing exceedence of water quality standards, and to allocate the total load among the sources of sediment in the watershed.