Minnesota’s list of water bodies that don’t meet state pollution standards has grown by another 581 lakes, rivers and streams.

The new additions to the Minnesota Pollution Control Agency’s biennial impaired waters list include a lower stretch of the St. Croix River, long considered one of the Upper Midwest’s most pristine waterways.

The MPCA said roughly 30 percent of the state’s lakes and 50 percent of its streams are listed as impaired because they have excessive levels of nutrients, don’t support aquatic life such as fish and bugs or aren’t safe for swimming and other recreation due to bacteria.

The MPCA must submit an updated list of the state’s impaired waters to the U.S. Environmental Protection Agency every two years. Over the past decade, the list has been steadily growing, as researchers examine the quality of more waterways across the state each year.

This year, the agency hit a milestone: It’s now monitored all 80 of the state’s major watersheds. That baseline data will be used to look for trends or signs of progress as researchers start the second round of assessments, said Miranda Nichols, who coordinates the impaired waters list for the MPCA.

Nichols said the number of newly listed impaired water bodies should start to decline, now that the initial round of testing is complete and state regulators can prioritize efforts to improve water quality.

“We’re looking for opportunities to start removing impairments,” she said. “We’re looking for trends and seeing how the work that’s been going on the last 10 years — seeing how it’s impacting the waters.”

The segment of the St. Croix River from the Taylors Falls dam to Lake St. Croix was added to the list because of high levels of phosphorus, which spurs algae growth. Most phosphorus comes from runoff from agricultural or urban areas.

The river’s listing isn’t a major surprise, because Lake St. Croix — the lower 25 miles of the river between Stillwater and Prescott, Wis. — had already been listed as impaired in 2008 for excessive phosphorus. Still, it’s an unpleasant label for a river long regarded as one of Minnesota’s natural treasures.

“I think it’s a wake-up call that what is done across this whole watershed has an effect on the river,” said Greg Seitz, publisher of St. Croix 360, an environmentally focused online publication. “And even if the river is protected as a [national scenic riverway] and has a lot of state and federal protections, water doesn’t know those boundaries.”

The St. Croix’s troubles didn’t develop suddenly in the past two years, but evolved over the years as fertilizer use and urban growth increased runoff into the river and its tributaries. Minnesota and Wisconsin have been trying to reduce phosphorus in the river for more than a decade.

The MPCA recently compiled the data needed to assess the river and found that its phosphorus levels exceed state standards, Nichols said. She said its listing highlights the importance of protecting the larger watershed that empties into the river.

“It’s coming off the land and into the river from upstream, from tributaries,” Nichols said.

Generally, water bodies in northeastern Minnesota are doing better than in western, central and southern Minnesota, where more urban areas and farms are affecting the water quality of lakes and rivers.

The vast majority — about 85 percent — of the impairments are the result of non-point source pollution, such as runoff from farm fields and urban areas or deposits from the atmosphere, said MPCA spokesperson Darin Broton.

“We’re entering into the harder part of all of this,” Broton said. “Now that we have a clear sense of what the impairments are in our lakes and streams and rivers, what do we need to do to actually move the needle to get these waters off the impaired list?”

That work has already begun. Once a lake or stream is added to the list, the agency develops a plan to restore the watershed and protect its water quality.

Money from the state’s Clean Water Fund, which receives funding from the Legacy Amendment sales tax increase Minnesota voters approved in 2008, helps pay for monitoring and for follow-up efforts by local agencies and landowners to improve water quality.

Restoration plans have been completed for 43 of the state’s 80 watersheds, and all should be done by 2023, said Paul Gardner, who oversees the state Clean Water Council, which decides how to spend the Clean Water Fund.

“The monitoring is just the first step,” Gardner said.

The MPCA is proposing to remove four water bodies from the list where restoration efforts have improve water quality: Sleepy Eye Lake in Brown County, Faille Lake in Todd County, Waverly Lake in Wright County and Plum Creek in Stearns County.

The public has until Jan. 14 to comment on the draft impaired waters list. Public meetings are planned around the state in December.

The MPCA plans to submit the list to the EPA by April 1.