SAN FRANCISCO (KPIX 5) — After exhausting all their options, San Francisco conservationists are turning to a fish-killing chemical to try and rid a lake of invasive species.

The chemical will be dropped in Mountain Lake, on the southwest corner or the Presidio, just off of 19th Avenue.

“Mountain Lake, we know, is about two 2,000 years old,” said Michael Boland, Chief of Planning Projects for the Presidio Trust.

After a century of neglect and abuse, the Presidio Trust is fixing Mountain Lake – which features no mountain and a body of water only slightly larger than a pond.

There are problems with the cleanup efforts – people have been putting their turtles, goldfish and other pets into the pond, where they have flourished. Nets, traps and stunning techniques have captured most of them, but as a last resort, conservationists plan to kill the remaining animals before restocking the lake with native fish.

“Rotenone is a naturally occurring substance that will kill the fish,” says Boland.

The remaining fish, invasive or not, still have little more time before the lake is cleansed. The presidio Trust says, that operation will begin at the end of this November. Rotenone is a plant-based chemical that is widely used to rid lakes of alien fish. All traces of the chemical, we are told, should disappear within three days.

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