With pants rolled up and shoes kicked off, people clamber across slippery rocks where the lake turns into a creek before it flows through a grove of trees.

It's a scene played out in lakes across Minnesota every summer, but this lake happens to be Itasca and the creek happens to be the Mississippi -- or its humble beginning, at least. The trickle meanders north toward Bemidji (which sits at a lower elevation), then east before barreling south to the Gulf of Mexico.

People come to this place, in Itasca State Park, to walk across the river. Several small foot bridges are in place for those who can't wade in the water but still want the experience.

The headwaters are marked with a sign that has the same design and wording of the original built by the Civilian Conservation Corps in the 1930s: "Here 1,475 feet above the ocean, the mighty Mississippi begins to flow on its winding way 2,552 miles to the Gulf of Mexico."

That's not exactly right anymore, said Sandra Lichter, a naturalist at the park. The changeable river is now about 2,318 miles long.

Some visitors drop a leaf or other item in the water, wondering whether it will make it to the Gulf and how long it will take. Lichter has an answer, for water, at least: the speed of the river at the headwaters is 1.2 miles per hour, so a drop of water at the headwaters would complete its long journey to the Gulf in about 90 days.