As drivers speed along Highway 1, past the Richmond District and into the Presidio, they might only catch a quick glimpse of Mountain Lake off to the east. But anyone who takes a stroll down to this small body of water, tucked away behind a playground and tennis court, will see one of the city’s only remaining natural lakes – and one of its oldest.
This 10-foot-deep lake, which historians date back as far as 2,000 years, has gone through drastic changes since its origins. In its early years, Mountain Lake was 40 percent larger than it is today: a 30-foot deep lake that provided fresh drinking water for the Ohlone Indians and European settlers.
Now it is filled with pollution and invasive, nonnative flora and fauna.
However, such agencies and organizations as the Presidio Trust, Friends of Mountain Lake Park, the San Francisco Zoo, volunteers and others are working to deepen and improve the health of this lake. Volunteers have already spent the last decade removing invasive eucalyptus trees and planting native willows, ribes, wax myrtle and red alder trees.
Genevieve Coyle, environmental remediation project manager for the Presidio Trust, a federal agency created to preserve and protect the Presidio, said the plan is to dredge 15,600 cubic yards of sediment from the bottom of the lake and remove the toxic substances that have seeped in over time.
Tractors, fencing and other equipment are already set up at the lake to begin the dredging in March, which will continue into October.
“This has been a long time coming and the community has been expecting it,” said Terri Thomas, director of cultural and natural resources for the Presidio Trust. “Now with the remediation happening, we’re going to try to get back the native fauna into the lake.”
One goal is to restore the western pond turtle, the only native fresh water turtle left in California, said Jessie Bushell, an assistant curator of the San Francisco Zoo, which is working with the Presidio Trust on this project. The turtle is listed as a species of special concern by the California Department of Fish and Wildlife, and must first have its proper habitat reestablished in the lake before it can live there again.
Mountain Lake was surrounded by grasses and shrubs – but very few trees — when Spanish Captain Juan Bautista de Anza and his soldiers arrived there in 1776. Wax myrtle and wet ground herbs, such as Apiacea and Ranunculaceae, were commonly found, according to Liam Reidy, an environmental geography student at the University of California, Berkeley, who studied the lake as part of his master’s thesis.
European settlers went on to use the area as grazing land. But prior to their arrival, the fresh water provided by the lake had made it an important campsite for Native Americans.
“The changes since have been very dramatic,” Reidy said. “It’s now one of the most contaminated lakes in North America.”
Mountain Lake began to fill in heavily after 1848, which was around the time the U.S. Army started taking over the property, said Dana Polk, senior advisor of media and government relations for the Presidio Trust. The Presidio, including the lake, was transferred from a military post to a national park in 1994 and became part of the Golden Gate National Recreation Area. Shortly thereafter, the Presidio Trust began working with the National Park Service to preserve the space.
One of the lake’s most recognized problems with pollution began in 1938 with the nearby construction of Highway 1. The lake filled with sediment during the construction and then storm drains sent roadway runoff directly into the water, Coyle said.
“Over a period of 70-plus years, the contaminants have washed directly from the road into the lake,” she said. “So lead at the bottom of the lake is believed to be from leaded gasoline use from back in the 1970s time frame.”
This lead was discovered during an environmental assessment that began in 2000 when the Presidio Trust had hoped to begin restoring the lake. But those restoration plans had to be put on hold until the lake was dredged.
“The lake was silting up and getting shallower and shallower,” said Rich Shrieve, president of the Friends of Mountain Lake Park. “In a few human generations it would revert to a meadow.”
He attributed part of the lake’s problems to dirt and debris that had fallen in over the years from the eucalyptus trees. But with the removal of these trees over the past decade and subsequent replacement to native riparian plants, Shrieve said, the area around Mountain Lake has already become healthier.
“Over the past eight to 10 years, we are seeing a lot of the birds coming back, and coyotes and other mammals,” he said. “It’s a city park, not a wilderness area. But there’s a real active, wild ecosystem in and around the park.”