This postcard was published in 1950. The long canoe race has not been held since 1960. There is an interesting article "Aquatennial Canoe Derby Was Test Of Stamina" about the race and Gene Jensen who was a race winner four times in 1948, 1949 1950 and 1960.
The description on the back of this postcard is as follows:
The Mando-Aquatennial Canoe Derby, co-sponsored by the Minnesota and Ontario Paper Co., is held in conjunction with The Minneapolis Aquatennial, the nation's greatest summer festival. It is now the world's greatest canoe racing event and attracts top-flight canoeists from all parts of the United States and Canada. Starting at Bemidji, Minnesota the course extends 450 miles down the challenging, unpredictable and ever-changing Mississippi River to end at Minneapolis.