because they cause the creation of deep pools, slowing the flow of flood water and enhancing fishery habitat. New beavers have recolonized Sonoma Creek and are currently located in both Sonoma and Glen Ellen. A "keystone species", the beaver have created habitat that has, in turn, led to the return of river otter ("Lontra canadensis") which have been sighted recently in the beaver pond below the Boyes Boulevard bridge in Boyes Hot Springs. Upland ecosystems drained include mixed California oak woodland, chaparral and savannah woodland, In these upland reaches one finds plentiful black-tailed deer, coyote, skunk, raccoon, opossum, wild turkey, turkey vulture, red-tailed hawk and occasionally bobcat and mountain lion. Prominent higher elevation trees include: coast live oak, Garry oak, Pacific madrone, California buckeye, Douglas fir, whereas valley oak is prevalent on the Sonoma Valley floor. History Up until about 1850, Sonoma Creek was unchanged from its natural state. Adverse erosion and bank cutting were at sustainable levels and did not add enough turbidity to the creek system to discourage aquatic species. Flooding in the downstream reaches did not realize the modern frequencies since all the creek reaches could absorb more excess water from peak rainfall events. The Kenwood area existed in the form of a large marsh effectively blocked by a natural earthen dam from penetrating the course of the creek as it flows west out of Kenwood toward Glen Ellen. With the advent of more intensive farming of Sonoma Valley in the latter half of the 19th century, the Kenwood Marsh was drained in favor of grazing, vineyards and other agricultural uses. This action removed the largest upstream buffer that assisted flood control in the lower reaches of Sonoma Creek. Consequently, the frequency and severity of modern floods (1960s onward) has been exacerbated by these interventions of humans. In 1978, Sonoma Creek was named a historic resource by the Sonoma League of Historic Preservation for being "one of the most picturesque sites and valuable natural resources in Sonoma County." Water quality The State of California Regional Water Quality Control Board considers the most significant water quality parameters in Sonoma Creek to be: turbidity, pathogens and nitrates. Turbidity is an issue because of historical problems of erosion of stream banks, especially in the presence of ongoing land development in Sonoma Valley. Increased sedimentation has a variety of adverse impacts including direct harm to aquatic organisms and the more specific