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For decades, it was a source of drinking water for the San Marcos area. Today, the South Lake Reservoir has new life as a local wildlife habitat.

South Lake was built with an earthen dam and provided drinking water to the Lake San Marcos area, most of downtown San Marcos, and the Coronado Hills area. Updates to potable water treatment had detrimental effects on the lake ecology, so the Vallecitos Water District stopped using the lake as a drinking water source in 1984, although it remained an emergency water supply for another decade.

Now, South Lake provides a thriving ecosystem within and around the facility. The lake is home to freshwater fish and abundant aquatic plant life. Waterfowl such as coots, gallinules, grebes, various species of ducks, and cormorants frequent the lake throughout the year. The property is filled with quail, doves, deer, rabbits, raccoons, skunks, squirrels, bobcats, and coyotes.

Volunteers help identify habitat and wildlife at South Lake

Vallecitos Water District staff recently surveyed the area to look for animal tracks and other signs of wildlife, and to catalog plant and animal species.

Certified California naturalists Paige DeCino and Karen Merrill from Preserve Calavera assisted Vallecitos public information representative Alicia Yerman, who is also a certified naturalist. The team spent three days exploring the lake and the 1.4-mile trail. Merrill and DeCino host the volunteer UC Naturalist certification program. The program is currently on hold due to the coronavirus pandemic.

Two wildlife cameras were set up at South Lake to capture wildlife activity over a two-week period. Lisa Urabe, a University of California trained Master Gardener and Vallecitos public information representative, asked the Buena Vista Audubon Society to conduct a bird survey. The BVAS volunteers identified 36 species in mid-February and created a YouTube video showcasing some of the species.

BVAS volunteers were enthusiastic about surveying the birds in an area set aside as wildlife habitat. With increased habitat fragmentation, BVAS hopes the area will remain primarily an area for wildlife.

“What you have at South Lake is a gem of the healthy functioning habitat— flora, fauna, and it is just a complete picture of what we hope our open spaces and natural lands to be,” said Karen Merrill. “It is something we should treasure now and into the future. It is one of a kind here on coastal San Diego County.”

Vallecitos employees take pride in the lake and its surrounding ecosystem and strive to keep the habitat intact for generations to come.

Firefighting helicopters can pull water from the lake

In addition to its value as local wildlife habitat, South Lake is available for fire suppression. Firefighting helicopters can pull water from the lake during wildfire events. The lake may be used as part of the City of San Marcos’ park system in the future.

Water quality within South Lake is monitored daily by water distribution operators, and the condition of the dam’s integrity is recorded weekly. Recently, an environmentally-sound ultrasonic technology made by LG Sonic was placed on the lake to reduce algae blooms and to improve water quality.