As members of the Presidio Trust stand on a fingernail of beach on the southern shore of Mountain Lake, an excited San Francisco resident stops by to comment on the organization’s lake restoration efforts. 
 
“This looks a lot better,” he yells, looking out over the only natural lake in the Presidio of San Francisco, a former U.S. Army base that became a part of Golden Gate National Recreation Area in 1994. Since 2001, the Presidio Trust, a federal agency created to preserve and transform the Presidio, has been working to make this little urban oasis healthy and functional again. 
 
Mountain Lake is adjacent to the West Coast’s high-traffic Highway 1, a busy golf course, and the Richmond neighborhood of San Francisco. These lively urban areas have contributed to degradation of the lake’s water clarity. In addition, the ecosystem’s biological diversity has been affected by non-native plants and animals that have pushed out indigenous species.
 
Terri Thomas, the Presidio Trust’s director of conservation, stewardship and research, points to the lake and a section of shoreline that used to be ringed by non-native eucalyptus trees. 
 
“After we took the eucalyptus out, the lake got clearer,” she says.
 
The removal of the eucalyptus trees was part of the first phase of restoration work at Mountain Lake. The initial phase also included weeds being removed and 14,000 native plants being planted. Restoration volunteers include Presidio Park Stewards, local students, corporate groups, and Friends of Mountain Lake Park. 
 
Thomas then points to traffic zooming by on Highway 1, perched right above the body of water. 
 
“We have spent the last 15 years trying to remediate the bottom of the lake from lead and contaminants from the highway,” she says.
 
In addition to polluting the water, the highway runoff contributed to changing Mountain Lake’s depth from 9 meters (30 feet) to just 3 meters (10 feet). 
 
The lake has also shrunk from the size when the Anza expedition camped beside the body of water in 1776. The Anza expedition was an exploration of California led by Mexican-Spanish explorer Juan Bautista de Anza. 
 
“We think [the lake's size] has been reduced about a third,” Thomas says.
 
Between September 2012 and December 2013, the Mountain Lake was dredged. The effort removed 13,380 cubic meters (17,500 cubic yards) of contaminated sediment, which was relocated to a nearby landfill.
 
Reintroduction Research
 
While standing on the shore, Jonathan Young, a wildlife ecologist interning for the Presidio Trust, spots a carp moving along the shallows. 
 
“That would be so easy to get,” he says, clearly wishing he had a net to nab the non-native. 
 
Getting rid of Mountain Lake’s carp is one of the biggest challenges to the Presidio Trust’s restoration efforts. 
 
“Our biggest problem is that there are non-native fish that damage the bottom and the vegetation,” Thomas says.
 
Young notes that being a natural space within an urban area means that over the years, San Franciscans have deposited non-native turtles, frogs, and fish into Mountain Lake. 
 
“This is a repository for people’s pets,” he says.
 
The Presidio Trust initially used electrofishing in an attempt to eradicate the carp. The method uses electricity to stun fish that are then pulled out of the water with nets. Currently, Young uses gill nets to remove the carp from Mountain Lake. 
 
After the carp are removed from the lake, they are transported to Al Wolf at the Sonoma Reptile Rescue Center in nearby Sebastopol. 
 
“He adopts them out to private, secluded vineyard ponds, where they won’t cause the same issues up there as they do down here,” Young says.
 
Once these non-native species are removed, the Presidio Trust can begin reintroducing native species back to the lake. Young says the organization has been looking at museum records and other documents to see what native species used to call Mountain Lake home. 
 
“We were able to get an idea of plants and animals that used to be in the area,” he says.
 
The Presidio Trust hopes to begin with placing Pacific chorus frogs, western pond turtles, freshwater mussels, Pacific newts, and three-spined stickleback (a small fish) back into Mountain Lake and the surrounding land. Eventually, they hope to welcome the endangered California red-legged frog. They are hoping to start reintroducing the three-spined stickleback in late 2014. 
 
The organization still needs to do more work to get Mountain Lake ready for the fish. 
 
“First, we need to remove all the predatory invasive fish, while at the same time, get the submerged plants [back in the lake], which will provide needed habitat for the sticklebacks,” Young says. 
 
The group has already begun putting aquatic plant species back into Mountain Lake. They place the seeds and roots of the plants in mud balls that are then thrown into the lake. Cages are then erected around the mud balls and vegetation so carp cannot de-root them while foraging for invertebrates that live in and around the new plants.
 
The restoration is a complicated process that relies on goals having to be met before the native plants and animals can be reintroduced. 
 
“It’s a really dynamic project,” Young says. “There are a lot of layers to it.”
 
Since Mountain Lake is a natural feature surrounded by a city, its successful restoration depends on local residents who use the park. 
 
“Ultimately, urban restoration projects like this,” Thomas says, “depend on the community.”
Lake Effects
The Presidio Trust is restoring a rare natural lake in the urban area of San Francisco.
adjacent
Adjective

next to.

aquatic
Adjective

having to do with water.

army base
Noun

facility owned and operated by an army, housing troops and equipment.

carp
Noun

freshwater fish native to Europe and Asia.

city
Noun

large settlement with a high population density.

Noun

management of a natural resource to prevent exploitation, destruction, or neglect.

contaminant
Noun

harmful or toxic substance.

contaminate
Verb

to poison or make hazardous.

degradation
Noun

breaking down.

Noun

difference.

dredge
Verb

to remove sand, silt, or other material from the bottom of a body of water.

dynamic
Adjective

always changing or in motion.

ecologist
Noun

scientist who studies the relationships between organisms and their environments.

Noun

community and interactions of living and nonliving things in an area.

electricity
Noun

set of physical phenomena associated with the presence and flow of electric charge.

eradicate
Verb

to destroy or remove.

erect
Verb

to build or raise.

expedition
Noun

journey with a specific purpose, such as exploration.

exploration
Noun

study and investigation of unknown places, concepts, or issues.

federal
Adjective

having to do with a nation's government (as opposed to local or regional government).

forage
Verb

to search for food or other needs.

functional
Adjective

usable.

gill net
Noun

effective type of fishing net that is suspended vertically in water by weights and floats. Fish are caught as they try to swim through.

Noun

environment where an organism lives throughout the year or for shorter periods of time.

Adjective

characteristic to or of a specific place.

initial
Adjective

first.

Noun

type of plant or animal that is not indigenous to a particular area and causes economic or environmental harm.

invertebrate
Noun

animal without a spine.

Noun

body of water surrounded by land.

landfill
Noun

site where garbage is layered with dirt and other absorbing material to prevent contamination of the surrounding land or water.

lead
Noun

chemical element with the symbol Pb.

Noun

an area within a larger city or town where people live and interact with one another.

non-native species
Noun

a type of plant or animal that is not indigenous to a particular area. Non-native species can sometimes cause economic or environmental harm as an invasive species.

Noun

area made fertile by a source of fresh water in an otherwise arid region.

perch
Verb

to sit or rest on a tree branch or other elevated position.

predatory
Adjective

killing other animals for food.

preserve
Verb

to maintain and keep safe from damage.

presidio
Noun

military fort or garrison.

remediate
Verb

to correct (remedy) damage to the environment.

repository
Noun

place where things are stored or deposited.

restoration
Noun

repair of damage to an ecosystem so that it can function as a normal self-regulating system.

root
Noun

part of a plant that secures it in the soil, obtains water and nutrients, and often stores food made by leaves.

Noun

overflow of fluid from a farm or industrial factory.

secluded
Adjective

sheltered, protected, and isolated.

Noun

solid material transported and deposited by water, ice, and wind.

submerge
Verb

to put underwater.

traffic
Noun

movement of many things, often vehicles, in a specific area.

transport
Verb

to move material from one place to another.

Noun

developed, densely populated area where most inhabitants have nonagricultural jobs.

vegetation
Noun

all the plant life of a specific place.

vineyard
Noun

agricultural area with grapevines grown for wine.