The south coast garter snake ranges throughout the United States and Canada. Along the Southern California coast it has a restricted distribution from the Santa Clara River Valley south to San Pasqual, San Diego County. It occurs in the Lake Prado Basin within the Upper Santa Ana planning area.

Habitat for the snake includes permanent water, low gradient topography and dense multi-storied riparian vegetation. They are restricted to shallow freshwater aquatic habitats such as wetlands and marshes. It requires open water for foraging and feeds primarily on amphibians, but also fish and invertebrates. The south coast garter snake breeds between April and November.

The primary threat to the south coast garter snake is habitat loss and degradation. Other threats include nonnative aquatic predators. Management includes habitat protection and enhancement by the removal of nonnative plant and animal species.