More streams and lakes in the vast St. Croix River watershed have landed on Minnesota's latest impaired waters list. Forty-two waterways were added this year, bringing the total to 174.

"We're seeing more waters listed because we definitely are seeing more intensive monitoring," said Chris Klucas, a St. Croix basin project manager at the Minnesota Pollution Control Agency. "I think the impaired tend to outweigh the unimpaired."

Water quality in the St. Croix basin has emerged as an urgent concern in recent years because of phosphorous concentrations that threaten the river's biodiversity. Lake St. Croix, the wider and deeper part of the river from Stillwater to Hastings, joined the state's impaired list in 2008 after monitoring of water quality showed excess phosphorus had created large oxygen-sucking algae blooms.

The dozens of tributaries that feed the St. Croix vary in quality. Many are challenged by urban encroachment and farm runoff. But the good news is that several new scientific studies are being done to identify the problems, Klucas said.

Still, the St. Croix River is "definitely in danger" of losing its reputation as a pristine waterway if the current trend continues, Klucas said.

"We can still make changes. We can still correct it," he said.

The St. Croix, which empties into the Mississippi River at Denmark Township and Prescott, Wis., collects water from a giant basin that stretches into Anoka County to the west, nearly to Duluth in the north, and far into northwestern Wisconsin. The shape of the basin resembles a map of Africa.

Being a good neighbor

Water drains into the river from streams, wetlands and lakes. Runoff from parking lots, streets and yards also finds its way to the St. Croix, putting everyone who lives and works in the river basin in a position to improve water quality.

"Water goes somewhere, whether you drink it or not," Klucas said. "Everything drains through groundwater. Watersheds are based on topography and drainage.... You need to be a good neighbor. It's all part of being part of a community, being a good steward."

As major rivers go, the St. Croix remains cleaner than most others in Minnesota. The Mississippi, Minnesota and Red rivers, for example, have more listed impairments. But the St. Croix's deteriorating water quality has inspired a flurry of studies and improvements in watershed districts up and down the river. Government scientists do some of the monitoring. Trained volunteers do the rest.

A year ago, the MPCA released a report, known as a Total Maximum Daily Load study, that seeks to reduce phosphorous contamination in Lake St. Croix to 360 metric tons a year -- the same as 1940s standards. Without corrective action, the study concluded, phosphorous contamination could reach 540 metric tons a year by 2020. The report called for public activism up and down the river to counter declining water quality.

Fertilizers, animal waste, storm-water runoff and other pollutants threaten recreational pursuits such as fishing unless all of the people who depend on the river rally to repair it, the report concluded.

Some improvements cited

"A lot of the work for these impaired waters is already taking place," Klucas said. For example, McKusick Lake in Stillwater was removed from the impaired waters list this year because of efforts in the watershed to reduce phosphorous contamination, he said, although he acknowledges that many residents remain unhappy with the lake's condition.

A small portion of the Sunrise River in Chisago County also fell off the list, he said.

But even as some waterways improve, others decline. Several small lakes in the Valley Branch Watershed District in south Washington County were added to the impaired list this year, Klucas said.

Biologists look for negative changes in aquatic life, such as sudden disappearances of dragonflies and other bugs essential to fish survival. Mercury and PCBs in fish tissue result in consumption warnings to anglers. Nitrates suggest evidence of excessive fertilizer runoff. Chlorides mean that road salt is washing into the river.

Residents in the St. Croix watershed can help the river with simple preventive practices, Klucas said: Don't cut down native trees and plants. Don't overapply fertilizer. Keep leaves and grass clippings off streets to reduce phosphorus. Make sure septic systems are up to date. To prevent bacteria problems, avoid leaving pet waste and livestock manure near the river.

"What you do may have an impact downstream," Klucas said. "To get these off the list, it's going to take citizens to make the changes. It's definitely a far-reaching watershed."

Kevin Giles • 651-925-5037; Twitter: @stribgiles