PARK RAPIDS, MINN. – The mating dance of the hex mayflies drew John Sorenson to the Straight River at sunset.
As the bugs floated like snowflakes in the fading summer light, he pulled on his waders and waited patiently for the distinct sound of trout breaking the dark water to feed.
"It's a treasure," he said, stepping to the edge of the grassy bank and casting his line, as he has for years.
But the Straight River is becoming warmer and more polluted as farm irrigation rigs multiply along its banks. Now Sorenson fears that the fish huddling in the cooler deep spots are a stark sign that northern Minnesota's only naturally producing trout stream is in trouble.
"In ten years the Straight River could be a big muddy stream good only for carp," he said.
And the peril is flowing downstream — into the Mississippi River and across a watershed that covers almost half of Minnesota, signaling a new and rising threat to one of the state's great natural wonders. Like many others across Minnesota, the great river is heading toward an ecological precipice.
In the last five years, the Upper Mississippi watershed has lost about 400 square miles of forests, marshes and grasslands — natural features that cleanse and refresh its water — to agriculture and urban development. That's an area bigger than Voyageurs National Park and represents the second fastest rate of land conversion in the country, according to one national study.
That breathtaking transformation is now endangering the cleanest stretch of America's greatest river with farm chemicals, depleted groundwater and urban runoff. At this rate, conservationists warn, the Upper Mississippi — a recreational jewel and the source of drinking water for millions of Minnesotans — could become just another polluted river.