Jonathan Young, a San Francisco State graduate student in biology and ecological restoration intern at the Presidio Trust, has the job of trying to restore some semblance of native life to Mountain Lake, in San Francisco’s Presidio. But as this sequence of photos shows, the native three-spined sticklebacks and Pacific chorus frogs he’d like to restore would face some ferocious predators lurking in the watery depths. So it’s Young’s job, for now, to try and get the predators out.

It’s a tough — perhaps impossible — task for a lone man with a fishing net. Mountain Lake covers about 4 acres and is around 10-12 feet deep, small in the grand scheme of things, but that doesn’t seem to have harmed its ability to support, for example, this very very big carp:

Young says a single carp can have two million eggs … in a season. There are probably 30-70 carp in the lake, he says, and if you remove 20 of them, as he did last year, well, “you do the math.”

Carp, bass, and mosquitofish are the main invaders in the lake. They didn’t get there on their own: most were released intentionally back when fishing was allowed on the lake, or by pet owners. (Young and others at the Presidio Trust have plenty of fishing already on their resumes and ask please please please don’t dump any more aquarium goldfish out there.) Sometimes people come into possession of rare, incredible monster fish, so unfortunately it follows that sometimes a rare, incredible monster fish shows up in the Mountain Lake net. Like this sturgeon.

“I have this tiny little inflatable raft, just for one person, and half of you hangs off in waders,” Young said. “I was out there early morning, all by myself, and this dinosaur comes out of the depths. It was bigger than the boat was, and it was freaking out. It was like a rodeo.”

The scene, he said, was simultaneously chaotic and hysterical: “I had to collect this five-foot long fish going crazy on my lap in this tiny boat I totally could have fallen off of. Very awkward, but very comical at the same time.”

The carp, sturgeon, many other big fish, and a wide variety of nonnative turtles that Young has collected over the years have been kept in pens and then shipped north to Sebastapol, where a distributor sends them to live out their lives in retirement in small ponds in the vineyards of Napa and Sonoma. Don’t worry if you haven’t received yours yet; Young says there’s plenty more where that came from.

“I pulled up a net the other day with a sturgeon scale bigger than the one the size you saw,” he said. “There’s a huge giant monster in there that got stuck in the net and ripped itself out. Who knows what’s lurking down there. It makes me freaked out every time I step in there in waders by myself, like something’s going to suck me down.

Part of what makes this photo series so compelling has to be Young’s expressions. There’s a Mona-Lisa-esque quality about his look. Is that uncertainty? Fear? Amusement? Derision? Boredom? Here is Young, for example, the corner of his mouth just curling downward — sfumato or just San Francisco fog? — his eyes slightly wide, as he holds up a half-dozen netted largemouth bass.

Maybe that’s because each photo is a surprisingly complicated act, Young says. Running through his head is the probable-impossibility of the task, the grandeur of the vision the task fits into, the humanity of yanking another living thing out of the water (even if it’s meant to live on elsewhere), the necessity of yanking the thing out so that some other thing can move in, the weirdness-with-just-a-touch-of-silliness about the scene of a guy in waders holding a monster prehistoric fish.

“A lot of people when they take pictures, they just automatically smile,” he said. “But I’m not happy about it. It’s just like, let’s take this picture and get it over with. It’s not like I’m flaunting this trophy.”

Bay Nature previously covered Mountain Lake’s renewal in February 2013: http://baynature.org/articles/bringing-life-back-to-mountain-lake/. For more on the project, see the Presidio Trust’s Mountain Lake project page: http://www.presidio.gov/about/Pages/mountain-lake-remediation.aspx.