On 19 June 2011, Cornthwaite began a , Guinness World Record-setting journey down the Mississippi River from source to sea on a stand up paddleboard. The journey started at Elk Lake, just south of Lake Itasca, in Minnesota. The descent of the Mississippi River took 68 days including passage through falls, dams and locks. Hurricane Lee caused Cornthwaite to leave the water for a time, lengthening the trip to a total of 82 days. Cornthwaite carried all of his provisions by securing them in waterproof bags strapped to the deck of his paddleboard. Cornthwaite's speed depended on that of the current. The greatest distance covered in one day was , just upstream of St. Louis.