The lake is currently used as a local wildlife habitat
and for fi re suppression, as fi refi ghting helicopters pull water from the lake during wildfi re events.
Future possibilities for the lake revolve around
recreational uses.
South Lake Reservoir
The South Lake Reservoir provided drinking water
to the Lake San Marcos area, most of downtown
San Marcos, and the Coronado Hills area until 1984
when the District’s wholesale water provider changed
their disinfecting chemicals. The new chemistry had
detrimental effects on the lake ecology, so the District stopped using the lake as a drinking water reservoir.
The lake was used solely as an emergency water supply
until the early 90’s when the State of CA Department
of Public Health determined that the water would not
meet their newly updated drinking water standards.
The District determined that it would not be fi nancially feasible to install the water treatment infrastructure
necessary to meet their requirements, so the lake was
no longer used as an emergency source.
patrolled by District personnel and the Sheriff’s
Department to deter trespassers and vandals.
An aeration system runs along the bottom of South
Lake to prevent the lake from “turning over.”
The air
bubbles rising up through the water keeps the water
circulating and prevents thermal layers from developing.
Without the air, anaerobic bacteria can fl ourish on the bottom layer of the lake producing hydrogen sulfi de
if these layers were allowed to develop. As winter
approaches, the top layer cools and can become
equal to or colder than the bottom layer. Water is
heaviest at around 39 degrees Fahrenheit and will
sink once the top layer becomes heavier than the
layers below. With the help of some wind, the layers
can change places and the lake can “turn over.” This
can result in many fi sh deaths and a rotten egg odor
that can be smelled by anyone who comes within
a mile of the reservoir. The aeration system is run
year-round to prevent this from occurring.
South Lake provides water for a thriving ecosystem
within and around the facility. The lake itself is home to fresh water fi sh with aquatic plant life in abundance along the shoreline. The surface of the lake is home
to Mud Hens, Mallards, and even Canadian Geese
on occasion. The land around the lake is fi lled with
quail, doves, rabbits, squirrels, and coyotes.
The District employees that care for the lake and its
surrounding ecosystem strive to keep the habitat intact for generations to come and hope that the community
will help preserve this small oasis of nature.
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South Lake 1959 South Lake today
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The water quality within South Lake is monitored daily
by water distribution operators and the condition of the dam’s integrity is recorded weekly. The lake is also
South Lake is capable of holding 73 million gallons
of water at maximum capacity. The lake is fi lled by
natural runoff from rain, so it is typically less than half full and even less than that during drought years.