Supply and Demand Assessment (SDA) – Petaluma River Watershed

The Petaluma River is one of the major tributaries to the San Pablo and San Francisco Bays. The watershed covers approximately 198 square miles, and its elevation ranges from sea level to approximately 2297 feet. The headwaters and tributaries of the Petaluma River originate on the southwest slopes of Sonoma Mountain, the southern slopes of Mecham Hill, and the eastern slopes of Weigand's Hill and Mount Burdell. The river flows through the city of Petaluma, then continues south-southwest into the northwest portion of San Pablo Bay. The watershed has a Mediterranean climate with distinct wet and dry seasons, and the land cover is mainly grassland and developed.

The Petaluma River watershed represents an important habitat for native aquatic species and spawning ground for anadromous fish, especially chinook salmon and steelhead trout. The decline in anadromous fish populations within the Petaluma watershed has been linked to increases in sedimentation, habitat degradation, and elevated stream temperatures. The Petaluma River has appeared on the Clean Water Act’s 303(d) list of impaired waters due to elevated levels of fecal indicator bacteria. The river is also listed as impaired due to excessive algae growth, known as eutrophication, a process that depletes oxygen levels and degrades aquatic habitats caused by high nutrient concentrations. These factors led to the development of a Total Maximum Daily Load (TMDL) for bacteria in 2019.