The Salton Sea, California is a large (980 km2), saline (43 g/l), closed basin lake that is fed primarily by the New and Alamo Rivers. These inflows enter into the southern basin where currents move in a roughly circular counter-clockwise pattern. The Sea is plagued with frequent algal blooms, some of which have been implicated in recurrent bird and fish mortality events. Increased water column stability and large nutrient inputs from these rivers may stimulate phytoplankton growth and may also affect zooplankton density in nearshore areas downcurrent from points of inflow. To assess the influence of these inflows on plankton dynamics, phytoplankton and zooplankton samples were collected at 17 sites around the perimeter of the southern basin at the 5 m isobath on two dates. Estimated current speeds and phytoplankton growth rates were also used to predict expected increases in phytoplankton density. In general, predicted increases overestimated actual downcurrent increases in phytoplankton abundance on both dates. However, taxonomic groups (e.g. diatoms, dinoflagellates) responded differently to the inflows. With the exception of one species, zooplankton abundances were similar at all sites. Differential responses among phytoplankton taxonomic groups were likely due to factors such as turbulence and cell morphology of individual species. Studies of the Salton Sea that focus strictly on midlake phytoplankton may miss important dynamics that occur nearshore. Phytoplankton blooms stimulated by river inflow may be redistributed to other regions of the lake and may adversely affect the large populations of fish and waterbirds that utilize southern nearshore areas.

Key words: phytoplankton bloom, river inflow, saline lake, Salton Sea, zooplankton