five centimeters can be attained. Range The precise historic distribution of Syncaris pacifica is not known, since geologic and climatic changes since the early Quaternary Period have significantly altered river courses of the Northern California coast. Historically, Syncaris pacifica may have occurred as far north as the Klamath River, but reductions of habitat, especially from overgrazing of cattle, along with chemical water pollution has greatly diminished the present range to 17 stream segments in Sonoma, Napa and Marin Counties. These habitat stream segments are sometimes separated by degraded portions of a given creek, effectively leading to a fragmented population. Occurrence is restricted to perennial streams below 100 meters above sea level in elevation and of gradient less than one percent. The stream segments can be grouped as follows: Certain stream segments which drain directly to the Pacific Ocean, including Tomales Bay, in Marin and Sonoma Counties Sonoma Creek, lower Napa River, Tolay Creek and Petaluma River, all of which drain to the San Pablo Bay Certain lower tributaries of the Russian River including the Laguna de Santa Rosa and certain of its tributaries such as Blucher Creek Habitat and behavior California freshwater shrimp prefer streams that have water flowing year round with predominately low gradient flows. In the summer months with little precipitation and surface runoff the flow rates can be very low with larger pools but they characteristically transport heavy runoff during the rainy winter season. Within a given stream, S. pacifica prefers slow- to medium-flowing pools and glide areas with overhanging banks. They do not inhabit even slightly brackish stream segments, but have been found to survive a minimum of 13 days in 50% seawater, perhaps allowing seed populations to colonize nearby streams as was possibly seen in Olema Creek. As a slow moving species S. pacifica feeds on decomposing vegetation and other detritus, consuming minute diverse particles conveyed by currents to downstream pools. As the water slows, the particles are filtered by the fine network of exposed roots from trees, such as from willows and alders. The California freshwater shrimp merely brush up the food with tufts at the tips of their small claws, and lift to their mouths the collected morsels. Colonized by algae, bacteria, fungi, and microscopic animals, the particle agglomerates are quite nutritious. Although most species of shrimp walk slowly about the roots as they feed, S. pacifica will undertake short swimming bursts to