Presidio takes first steps to rejuvenate Mountain Lake 

click to enlarge A woman and child explore the shore of Mountain Lake, one of three remaining natural lakes in San Francisco, Thursday. - MIKE KOOZMIN/SF EXAMINER
  • Mike Koozmin/SF Examiner
  • A woman and child explore the shore of Mountain Lake, one of three remaining natural lakes in San Francisco, Thursday.
San Francisco is reviving a slice of its natural history one fish, frog and turtle at a time.

For more than a decade, ecologists have strived to return Mountain Lake — one of three remaining natural lakes in The City — to a healthy body of water. The cleanup efforts follow years of contamination caused primarily by sediment from state Highway 1, which cuts through the Presidio to the Golden Gate Bridge.

After the removal of invasive plants and animals, as well as cleaning up a half-dozen feet of residue at the bottom of the lake, Presidio Trust officials recently introduced the first native species back into the waters. The 153 three-spined sticklebacks that call Mountain Lake home as of April 1 are the only fish species native to the lake. They were harvested from Lobos Creek, also in the Presidio, and some are believed to have already laid eggs.

“They dispersed almost immediately and are now hopefully starting to breed,” said Jonathan Young, a wildlife ecologist for the Presidio Trust. The fish provide insect control and food for native birds and reptiles.

They disappeared from Mountain Lake when predatory nonnative fish such as bass and carp were introduced, likely from recreational fishing in the 1800s and 1900s, and from aquatic pets abandoned by their owners.

In fact, pet desertion remains perhaps the greatest threat to the continued vitality of Mountain Lake, Young noted.

“One breeding pair ... could stir up a whole population of unwanted animals that would reduce the health of the lake back to where it was,” Young said.

Wildlife officials are focusing on educating the public to help curb unwanted animals and plants in the lake, which can spread disease and consume the native ecosystem. In mid-January, the Presidio Trust installed a drop box at Mountain Lake for unwanted fish and other aquatic animals.

To date, two turtles and three fish have been left in the lake’s holding tank. The box is checked daily by the Presidio Trust, and the discarded animals are taken to a sanctuary.

In a city once peppered with lakes, ponds, creeks and other sources of aquatic habitats, introducing native species back into Mountain Lake marks the restoration of a small but significant piece of old-time San Francisco, Young said.

“It’s a very rare system, and it’s a very classic example of San Francisco natural history,” he said. “It’s impossible to get [the lake] to what it once was, [but] the goal is to restore it in a way that allows it to remain healthy and functional.”

Wildlife officials expect to release the next native species, a batch of Pacific chorus frogs, into Mountain Lake within the next month. Western pond turtles and California floater mussels will be reintroduced later this year.

About The Author

Laura Dudnick

Bio:
Laura Dudnick, a Bay Area native, covers education and planning for The San Francisco Examiner. She previously worked as a senior local editor for Patch.com, and as the San Mateo County bureau reporter and weekend editor for Bay City News Service.
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