Minnesota state agencies and environmental groups have made reducing farm field runoff into fields a major priority.
But the task will be difficult, if the record May rains are any indication. Some parts of the state had almost a foot of rain last month, when six inches or more fell in a broad strip from southwest Minnesota to the Twin Cities, including the Mankato area.
That's where Minnesota Pollution Control Agency river monitoring coordinator Pat Baskfield videotaped the effects of an intense May 5 downpour. His video shows the rain water pooling and then draining away in a rapidly moving stream.
"In 20 minutes time, basically this field turned into a little lake at the bottom," Baskfield said. "Water was running across the field, on the edge of the field there was a gully forming so water rushed down that."
As the gully grew in depth, the water turned brown, picking up a growing amount of soil. Much of that eroded soil was bound for the Watonwan River.
The farm field was likely just one of hundreds, or perhaps thousands to lose soil in the intense May rainstorms. Baskfield said much of that eroded soil eventually found its way to a stream somewhere.
"You wash a lot of pollution into the rivers, it takes a long time for that to come out," he said. "We'll see a 25-minute rain event dirty a river up for two to three weeks."
The MPCA is still assessing the effects of the heavy May rains on Minnesota rivers. But the day after the downpour, Watonwan River sediment levels jumped to about six times what pollution control officials would like to see. The amount of phosphorus was about five times desirable levels.
The Watonwan flows into the Minnesota River, which carries the pollution to the Mississippi. Much of the soil settles out in Lake Pepin, which is rapidly filling in. Some goes all the way to the Gulf of Mexico.
"One thing directly affects another, and another and another and another and on and on," said Scott Sparlin, who founded the Coalition for a Clean Minnesota River more than 20 years ago. "And the complexity of all of it is perplexing." Sparlin, of New Ulm, was one of the first activists in the state to target farm runoff issues.
As the 61-year-old lead the way along Seven Mile Creek near St. Peter, he said the stream is another major contributor to Minnesota River pollution. He pointed to ravines gouged into the steep banks when the heavy May rains bolstered by farm field runoff carried soil, trees and other debris into the creek.
Cleaning the creek, the Minnesota River and tributaries downstream would require solving significant problems, he said. Chief among them is decreasing farmland runoff.
"How do we continue to grow the best crops in the world and have the best production in the world but at the same time not compromise our water quality?" Sparlin asked.
The good news, Sparlin said, is that in the last two decades farm pollution in the Minnesota River watershed has been reduced. But the decline is less than what MPCA officials want to see. He'd like to see more cropland that lies in flood plains converted to water absorbing grassy areas.
Sparlin also favors drainage systems designed to limit how much farm runoff reaches rivers. But such steps can be very expensive, and that keeps many farmers from adopting them. Also, many farmers question whether any measures can protect against the types of downpours seen this spring.
"Significant rainfall events, they're going to cause damage in one way or the other," Montevideo farmer Kirby Hettver said.
Hettver has experienced first-hand the difficulty of controlling runoff. He's a member of a new state committee working to encourage better on-farm practices to reduce how much water leaves fields.
"We're always looking at ways to make improvements or do things a little bit better," he said. "That will protect the environment and help meet the demands of Minnesota's consumers."
Hettver said some of the best steps are simple ones such as leaving lots of corn stalk or other plant residue on top of the soil. Over thousands or millions of acres, this minor change can hold back huge amounts of runoff. It will likely take efforts on that scale to make a difference for the state's rivers.