The Santa Margarita Watershed covers an area of approximately 154 square miles in southwest Riverside and northern San Diego counties. The watershed is primarily fed by rainfall and snowmelt from the Santa Ana Mountains. The watershed has a high potential for flash floods due to its steep terrain and low permeability of the soils. The snowpack in the watershed varies greatly from year-to-year, but typically peaks in March. The primary surface water sources in the watershed are the Santa Margarita River and its tributaries, which flow into the Santa Margarita Reservoir. The reservoir serves as a vital source of drinking water for the region. The reservoir contains a range of constituents, including sediment, nutrients, and algae. The region experiences a Mediterranean climate with hot, dry summers and mild, wet winters. In recent years, the region has experienced drought conditions, which have impacted water availability in the watershed.