"The basin of the Mississippiis the body of the nation."

Mark TwainLife on the Mississippi, 1883SCROLL

A RIVER AT RISK

The Mississippi is North America's greatest river. But in Minnesota, home to its headwaters, sweeping changes in the landscape are putting water quality at risk. From its headwaters in north central Minnesota, the Mississippi River winds 2,300 miles to the Gulf of Mexico, draining an area larger than continental Europe. It furnishes drinking water to at least 15 million Americans, serves as a flyway for 40 percent of the nation's migrating waterfowl and provides habitat for 25 percent of all North American fish species. Once considered the mythical dividing line between the settled regions of the East and the untamed West, the river has always served as a cradle of culture, transportation and trade in the region. Minnesota is home to the cleanest stretch of this great river — the Upper Mississippi, whose watershed sprawls from Bemidji to south of the Twin Cities. But today the Upper Mississippi faces a set of encroaching threats. Losing wilderness

Since 2008, the Upper Mississippi's watershed has lost some 400 square miles of forests, grasslands and wetlands — natural features that store and purify water. Wild lands are giving way to farming and housing, which alter runoff patterns and deliver more pollutants into waterways.Natural ground cover lost to row crops

(percent change 2010 — 2015)

Impaired waters

Many of the Upper Mississippi's important tributaries, and many lakes in the watershed, are now listed among the state's "impaired waters," according to the Minnesota Pollution Control Agency. Protecting wilderness

Recognizing these risks, conservationists and state agencies have identified parcels of land that are especially valuable in protecting water quality. Thousands of acres have been purchased or placed under permanent easements to preserve wilderness, mostly in the northern reaches of the watershed. A battle unfolds

Even so, a race to preserve forests in order to protect water is unfolding at a series of crucial spots where the Upper Mississippi curls through central Minnesota. Mississippi headwaters

Each year more than half a million visitors journey to Itasca State Park to see the origin of the revered waterway — a measure of how Americans treasure the Mississippi. An aquifer under stress

But just a few miles away, agriculture is placing new stress on the Pineland Sands Aquifer, an important source of groundwater for local streams and lakes. Irrigation has boomed, and farmers are pumping tens of millions of gallons of water annually from the aquifer. Paving paradise

Farther downriver, population is booming in the Brainerd area as more families and retirees seek a piece of northern Minnesota paradise. But that means more roads, parking lots, driveways and other forms of pavement that can increase polluted runoff. Irrigation creates new demands

And where the northern forests give way to farm fields around St. Cloud, an increase in irrigation is straining groundwater and streams such as Little Rock Creek, while contaminating drinking wells with farm chemicals. Preserving water by protecting land

All along the Upper Mississippi, there are ambitious efforts to preserve natural landscapes. One of the biggest projects is at Camp Ripley, where federal and state governments are joining forces to preserve hundreds of thousands of acres of forest around the confluence of the Crow Wing and Mississippi Rivers. Drinking water at risk

More than 1.5 million people in the Twin Cities and St. Cloud rely on the Mississippi River for drinking water. While that water is still remarkably clean, further deterioration in the river could mean that, like other communities around the state, the cities will have to install expensive water treatment systems. The Star Tribune examines the threats facing Minnesota rivers, and the struggle to redeem a natural treasure — the Mississippi — before it's too late. DANGER DOWNSTREAM

Coming Sunday, a special report at startribune.com/riversREAD THE SPECIAL REPORT