Watching the chattering brook - six feet wide and six inches deep - it is hard to picture the treacherous surge it will become as it makes its way through 2,550 miles of rapids, lakes and loops to the Gulf of Mexico.
It will expand to thousands of feet across, and 100 feet deep. When it reaches the end of its journey, it will expire dramatically by spewing 600,000 cubic feet into the gulf every second.
The first 750 miles of the river rumble through Minnesota and are arguably the most beautiful. Along the banks of the wilderness of the northern half of the state, wolves outnumber humans, crime is still rare, and pollution is something that happens to city folk a long way away. There are walking and cycling trails through the birch forests and remote campsites for those who want to sleep beneath the stars. Nature is very much in charge. Spring brings blankets of wild flowers and warm summers green the forest- a relief after an Arctic winter of deep snow and temperatures of -30C. In late summer and autumn, along the banks of the river, the trees turn colour, going from deep green to crimson, gold and bronze. Those tracing the river on "colour tours" by car, or, just as popular, on Harley-Davidsons, will see very little traffic - indeed, the highways are carpeted with fallen leaves.
But the best way to go is down the river by canoe. I hitched a ride in an aluminium dugout with Jessica Bussler, a third-year biology student at the University of Minnesota. It had been a dry summer and the river was running dangerously low - just a couple of feet in places. Shortly after Jessica had taught me about reading the river's ripples to avoid hidden boulders that can flip a boat over like a coin, I demonstrated my navigational prowess by crashing into a bank of rocks. The boat lurched violently to one side and jammed. Lesson One on the Mississippi River.
What had seemed a slow current easing us downstream was now a raging torrent smashing against the side of the canoe and trying to drown us. I clung on for dear life and tried frantically to free the boat with my paddle.
We shifted the canoe off the rocks just in time as the water started coming over the side. I collapsed, breathing hard, and let it drift to the shore of an island. I was shaking with adrenalin but Jessica just told me she was planning to canoe all the way to New Orleans after she'd finished college. I did not volunteer for helmsman.
Canoeing, white-water rafting and fishing are popular all year round in Minnesota, but you will need to pick your season because the river rises and falls considerably: high water in spring, swollen by snowmelt, and low water in autumn after a hot, dry summer.
The river sinks through small apple-pie towns where Charlie Brown might have grown up. Bemidji, just 90 miles from the Canadian border, is the home of the fictitious lumberjack giant Paul Bunyan and his blue ox, Babe. Legend has it that the Mississippi was created by Babe kicking over a pail of water at Bunyan's lakeside camp-fire. The water ran through Middle America all the way to the Gulf of Mexico.
Grand Rapids is famous as the childhood home of Judy Garland. You can peek at her house and walk a stretch of yellow-brick road outside The Old School House, where some bricks are inscribed with soppy messages from Munchkins and old friends. Despite this, the town is, thankfully, not a shrine littered with Wizard of Oz Gift Shops and Dorothy's Ice Cream Parlours. In fact, it must rank as one of the purest and least commercial towns in America. The air is fresh and invigorating and straight from the northern tundra, and the sunlight is a brilliant white.
Minnesotans call their state the land of 10,000 lakes and are proud of its history of pioneer survival.
You are nobody up here if you haven't got your own snowmobile and a 12- bore shotgun. During the hunting season, which starts in late summer, the woods are full of men wearing checked jackets and carrying enough ammunition to start a militia. Sometimes, it gets so crowded that they have to don bright orange caps so as not to mistake each other for deer. The list of huntable creatures in Minnesota runs the length of a sheet of A4; even moose are not safe. Tourists are just as welcome to try their luck as the locals.
When Bruce Ogle is not running his supermarket in Grand Rapids, he is out stalking deer, sometimes for days on end. I met him one morning. He wore a hat embossed with the logo of one of his shooting clubs - Ducks Unlimited. We drove a few miles out of town to Pheasants Plus, a clay-pigeon range, and, between deafening cracks from our guns, he gave me a hunting-history lesson.
"It's as common as going for a picnic or watching TV," he said. "Everybody does it here. There are more than half-a-million hunters in the state. It's in the blood."
I believed him. I had seen the newsagent's shelf groaning under the weight of hunting magazines with titles such as Attack, Bolt or Shoot, all full of pictures of hairy hunters with one foot propped on the haunches of their felled prey. In one shop, pubescent Beavis and Butthead lookalikes were reading them as intently as they might a porn magazine.
"You gotta remember that hunters have great respect for animals. We know deer are amazing and beautiful creatures but they are also beautiful to eat. We love nature and the outdoors a lot more than folks that don't hunt. Many people hunt over there, in England?"
I did not know where to begin on the great British hunting debate. I could imagine hunt saboteurs getting short shrift from these woodmen armed to the teeth, although there is a small animal-rights movement which is trying to apply pressure. Bruce threw open the back of his vast all-terrain vehicle and slid out two polished rifles and a sackload of shells.
"I guess this is the difference between England and the US. We protect our right to bear arms, always will. Government will never take that away."
In the days when that right was coming into being, American Indians and Europeans used to meet along the Mississippi and its tributary streams in their birch-bark canoes to trade knives and jewellery for furs.
Birch-bark canoes are still built up in the backwoods. On the shores of the Big Fork River stands Ray Boessel's workshop. Ray is the grandson-in-law of Bill Hafeman, a German immigrant who was the first white man to build the canoes in this area. He is carrying on the cottage industry and was stripping birch roots when I turned up, one lunchtime. We talked late into the afternoon, until the mosquitoes drove us into the workshop. Ray explained how traders would have paddled down the Big Fork River and portaged by foot to the Mississippi. Back then, provisions would have been vital because traders would have been away from civilisation for days on end.
His workshop was open to the public, although the visitors' book was only half full and a little out of date, which was a shame because the Hafeman boatworks was unreal, unspoilt, Minnesota heritage.
On the other hand, maybe it was a good thing that he wasn't overrun with tourists. After all, Minnesota is America's best-kept secret and Americans would very much like to keep it that way.
Matthew Brace paid pounds 505 for a return fare with British Airways (0345 222111) to Chicago, and then caught an Amtrak train from Chicago to Minneapolis- St.Paul (pounds 60 one way). North West Airlines (0990 561000) fly from London to Minneapolis-St Paul via various northern US cities; high-season prices are from pounds 523 plus pounds 47 tax.
Where to stay
The Nicollet Island Inn (612 3311800), on an island in the Mississipi in downtown Minneapolis ($115-$150 approx a night) makes an excellent base for touring the twin cities and central Minnesota. In Bemidji, try the cheap ($25 a night) but friendly Midway Motel (218 7511180). In Grand Rapids, best value is Rainbow Inn (218 3269655) at $40 a night.
Call the Minnesota Office of Tourism on 612 2965029; or consult their website on: www.exploreminnesota.com.