On the surface, so to speak, Colby Lake is one of several pretty bodies of water clustered in the western part of Woodbury, the focal point of nearby housing developments, encircled by a well-kept trail popular with joggers, bicyclists and dog walkers.
But serious problems have been lurking with the lake's water quality for years, and a broad-based effort is aiming to get the lake back into proper environmental shape by the end of next year.
The state Department of Natural Resources (DNR), South Washington Watershed District, the Washington Conservation District, the city and even homeowners near the lake are working in concert to achieve that goal.
"Everyone is working on different aspects of this — it's all about working together," said Jim Levitt, a fisheries specialist with the DNR who supervises the agency's Fishing in the Neighborhood (FiN) program. "It's about leveraging those local connections to do more with the limited resources that we have."
FiN has been managing the fish population in Colby Lake since 2002, Levitt said. It has been a slow and steady effort that will reach a key benchmark of progress when an 84-foot fishing pier — a T-shaped structure similar to those on Powers and Battle Creek lakes in the city — is installed on the south end of Colby Lake, probably by September.
The pier installation, which is planned at no cost to the city, comes a year after the watershed district installed an aeration system to keep oxygen in the lake and prevent the frequent winterkill of fish, Levitt said. With that and other steps, a lake once dominated by bullheads and white suckers will soon be giving way to bluegill, crappie and even northern pike.
The pier has been a priority for the FiN program. The program aims to increase angling opportunities, public awareness and environmental stewardship in the seven-county metro region. Ultimately, it works to keep the fishing tradition in Minnesota vibrant, particularly among young people, he said. A key aspect of that is to providing angling opportunities close to where people live.
Improving habitat is part of that mission, and Colby Lake clearly needed help.
The lake was listed as "impaired" by the Minnesota Pollution Control Agency in 2006, mostly because of the high content of phosphorus washed into it by stormwater runoff from the surrounding area. The phosphorus, in turn, causes a major algae bloom that chokes off oxygen for fish. The DNR's water quality summary lists it as "very green," and in the agency's grading system, it has consistently gotten D's and F's.
Shallow lake hurts quality
The lake's physical characteristics also work against it, Levitt said. It has a surface area of about 70 acres, yet its deepest point is only about 11 feet. Because of that shallowness, the entire lake is in what scientists call the "littoral zone," the top 15 feet of lake surface that is dominated by vegetation.
Also, the lake's watershed is nearly 8,100 acres, a watershed-to-lake ratio of 114:1 — a high number that increases the lake's potential for stress.
With installation of an aerator, stocking by the DNR and the addition of rain gardens in surrounding residential areas, Colby Lake should soon become more habitable for fish — and more attractive to anglers, who will have a pleasant place to wet their lines.
The DNR has typically stocked the lake with bluegills, crappie and perch. But last year and this spring, Levitt said, channel catfish were added to the mix, with the specific aim of cutting down on the population of bullheads on which the catfish prey.
"That will also help with water clarity," he said.
25 rain gardens
Some of the most effective efforts to clean the lake are happening offshore, in the neighborhood around it, said Angie Hong, educator with the East Metro Water Resource Education Program run jointly by Washington County, the conservation district, the county's eight watershed districts and eight cities.
Using grant money from the state's Clean Water Land & Legacy Fund, 25 rain gardens are being built to filter phosphorus and other pollutants in the runoff before they can reach the lake, she said. About half were installed last year, and the remainder will be completed by mid-July.
The rain gardens, using deep-rooted plants and grasses that absorb a lot of water, were installed at no cost to homeowners, she said, though they will take over responsibility for their maintenance.
Designers also worked with homeowners — whose properties were picked based on a study of surface water flow to the lake — so the rain gardens were a good fit with their property.
The city also had a role in the neighborhood effort, Hong added. In planning a recent street improvement project, roads were designed with boulevard strips so the roads could be narrower, thus cutting down on the amount of impervious surface that adds to runoff.