Study Lays Out Roadmap for Restoring Mt. Lake

By Peter Sciacca

A study released late last year provides a general blueprint for significantly restoring Mountain Lake and San Francisco's other two natural lakes. Pine Lake and Lake Merced. The report, sponsored by the Neighborhood Parks Council, breaks down the current state of each lake, what problems afflict them and what steps need to be taken to reverse decades of degradation.

"It (the study) focuses on bringing together community organizations, land owners and government agencies to protect water quality, watersheds, protect against flooding and restore habitats," said Katie Pilat, the study's author. She is the project manager and outreach coordinator for the San Fransquito Watershed Council.

Out of the 10 natural lakes that were in San Francisco, Mountain Lake, Lake Merced and Pine Lake are the only ones left. Laguna Honda technically still exists however, its bed was paved over and integrated into the city's reservoir system in 1863. The rest of the lakes were filled in. Despite the poor condition of the three lakes, they provide valuable natural resources for San Francisco.

"They are important to the remaining wildlife in the city and also are vital as recreational sites for residents," Pilat said. "They have been neglected far too long. Communities have to play a role in the management of these lakes."

Pilat's general recommendations for the lakes include monitoring what flows into them and determining the interaction between ground and surface water at each lake.

"(The amount of water the city and private organizations take from these lakes) also plays a large role," she said. "Plants are a factor because they dictate the rate of shoreline erosion. This directly affects the amount of sediments that build up at the bottom of the lakes."

Mountain Lake's woes began when Spanish settlers arrived about 200 years ago. Years of overgrazing by livestock, urbanization, road construction and the introduction of invasive vegetation have all taken their toll.

One of the lake's most serious problems is its shallow depth. In the last 100 years its maximum depth of 15 feet has dropped down to about 9 feet. Most of this can be attributed to the construction of the adjacent Park Presidio Boulevard approach to the Golden Gate Bridge in the late '30s. Countless tons of sediment were pushed into the lake during the span of the project.

The buildup of various chemicals in the lake from runoff has tainted its water. Two of the culprits are nitrogen and phosphorus, which are found in fertilizer. In large concentrations, these chemicals have been found to spur algae blooms and kill fish. Lead, zinc and copper runoff from the nearby road is Pilat's greatest concern.

"A group called the Mountain Lake Enhancement Team is working within the California Department of Toxic Substance Control guidelines to dredge and dispose of this debris," she said. "These guidelines make the project more complex than dealing with less toxic forms of waste."

The dredging of about four feet of sediment from the lake bottom to remove these and other chemicals is part of the first phase of the Mountain Lake Enhancement Plan. The project is designed to improve the lake's water quality, habitat and public access. The other two steps that are part of this initial phase areá carving out a designated path and replacing eucalyptus trees with native plants to reduce erosion on the lake's eastern shore and installing a mechanical aeration system on the lake bottom to temporarily improve water quality and oxygen flow. The installation of native plants and the removal of eucalyptus trees was completed earlier this year, but maintenance of the newly placed plants is ongoing.

Pilat said the first phase is almost complete. The second phase will focus on the eastern part of the lake.

"It is expected to involve further replacement of invasive plant species with native ones," Pilat said.

This phase will also include installing a bridge to replace the road that currently divides the eastern arm of the lake from the main body of water.

The final component of the plan seeks to divert roadway runoff so the lake is protected from future contamination.

"Negotiations are ongoing to find a solution for the runoff problem," Pilat said.

Mountain Lake is home to a variety of small animal species, such as birds and amphibians.

"Its close proximity to other natural areas is another reason why it is important to wildlife," Pilat said.