Storm water carries so much phosphorus into a chain of lakes in Maple Grove and Plymouth that it may take 20 years to get the three lakes off the state's impaired waters list.

That's the finding of a new report to the Minnesota Pollution Control Agency which describes the extent of the pollution in each lake and what can be done to reverse it. The report begins the process of cleaning up the lakes as required by the federal Clean Water Act.

In Eagle Lake, a 291-acre lake popular for fishing and swimming, phosphorus would have to be reduced by 40 percent to meet Clean Water standards for swimming, the report says.

Cleaning up two smaller connecting lakes would be an even bigger uphill climb. To meet clean-water standards in the 81-acre Cedar Island Lake, phosphorus would have to be reduced by 67 percent. The 58-acre Pike Lake would need a 49 percent cut in phosphorus.

Marred by algae, all three lakes were flagged for poor water quality that limits recreation. The state placed Pike Lake on the impaired waters list in 2002, Cedar Island Lake in 2004, and Eagle Lake in 2008. Currently, there are 1,475 total lakes and streams on the list in Minnesota. The list will be updated in 2010.

With the report establishing pollution levels, the Maple Grove and Plymouth lakes are now among the first to begin the cleanup process. Reducing their high phosphorus loads will require a lot of work, a lot of money and a lot of creativity, said PCA project manager Barb Peichel.

"They are very typical for urban lakes in the metro area where we had the rapid development back a few decades ago," Peichel said.

Sources of pollutants

Rain running off roads, parking lots and lawns gets pushed right into the lakes, Peichel said.

"Now we have to go back and figure out how can we get the rain water to go into the ground where the rain drop falls," she said. "It took time for the lakes to get polluted. It's going to take some time to get it cleaned up."

Strategies for limiting storm water running into the lakes include using residential rain gardens and collectors such as rain barrels; replanting parks and open space with native vegetation rather than maintaining mowed grass; frequent street-sweeping with dustless regenerative air sweepers; and creating native plant buffers along shorelines to filter out pollutants in place of grass or riprap.

Residents of Maple Grove and Plymouth have until Oct. 28 to comment on the state's report before it is sent on to the federal Environmental Protection Agency for approval later this year or in early 2010.

For people who live around the lakes, the comment period is an opportunity to point out any inaccurate information, register support for the process and look at what may be required under a pollution prevention plan. The report can be viewed at tinyurl.com/yb4dv2z.

"This is the first round of input for the residents, and it is important for those who are interested in water quality to take a look," said Derek Asche, water resources manager for Plymouth. "Now we know what the reductions [in pollutants] need to be, and we would really like the public to be engaged in the process."

The PCA will respond to comments, amending the report as necessary, and send it on to the EPA, which will have 30 days to review it and approve it, Peichel said.

After the federal government OKs the report, Maple Grove and Plymouth will have 18 months to decide which strategies residents and the city will use to reduce the pollution. The cities will hold public meetings to discuss cleanup options, Asche said.

The strategies that are chosen will be folded into each city's storm water pollution prevention programs, subject to the approval and enforcement by the PCA.

Is there reason to think lake water quality actually can be restored? "Time will tell," Peichel said. Over the next five to 10 years, the PCA will take stock of how lakes are doing and prescribe a different approach if necessary, she said.

Laurie Blake • 612-673-1711