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Staff Report — Update on the San Joaquin River Dissolved Oxygen Total Maximum Daily Load (TMDL) Introduction The Regional Board requested regular updates on the progress of the San Joaquin River Dissolved Oxygen Total Maximum Daily Load(TMDL) effort and has received four such updates since January 2000. The last update was given at the January 2002 Regional Board meeting, when a presentation was given by the Dissolved Oxygen TMDL Steering Committee on the development of their Plan of Action for proposing their own TMDL implementation plan and load allocation. At this last meeting the Regional Board requested another status report in about 6 months. Description of Impairment The San Joaquin River experiences regular violations of the Basin Plan water quality objective for dissolved oxygen in the Stockton Deep Water Ship Channel (DWSC) between Channel Point and Disappointment Slough. Low dissolved oxygen concentrations may act as a barrier to upstream spawning migration of Chinook Salmon and may stress and kill other resident aquatic organisms. In January 1998, the Central Valley Regional Board approved a 303(d) list identifying this dissolved oxygen impairment as a high priority. A number of studies in recent years have helped identify the major sources and the chemical and physical mechanisms linking them to the low dissolved oxygen problem. Although further study is required, the following main causes have been identified: • Algal matter and ammonia delivered from upstream agricultural and municipal sources decomposes in the DWSC creating an oxygen demand • The presence of the DWSC has increased residence time allowing more of the oxygen demanding substances to impact oxygen concentrations • Upstream diversions and routing of flow in the Delta to the State and Federal pumping projects has further reduced flows and increased DWSC residence times Stakeholder Process In April 1999,the Regional Board approved the Regional Bay Protection&Toxic Cleanup Plan (BPTCP),which outlined the formation of a Steering Committee consisting of representatives from various agricultural,municipal and environmental stakeholder groups. The Regional Board only has jurisdiction over entities that discharge chemical and physical constituents that lead to violations of water quality objectives. This low dissolved oxygen impairment, however, is caused additionally by the altered channel geometry of the DWSC and by reduced flow through the DWSC from upstream diversions. The Steering Committee process provides the stakeholders the opportunity to involve those entities responsible for the non-load related causes of the problem. This will help produce a more equitable distribution of responsibility among thosc actually contributing to the problem. Similarly, the BPTCP recognized that the most practical and cost-effective solutions to the problem might involve more than just control of constituent