There are different river trip opportunities through Grand Canyon National Park: half-day and full-day smooth water trips on the Colorado River or noncommercial trips that launch from Diamond Creek and takeout at Lake Mead typically are 2 to 5 days in length. These are also professionally guided raft trips, available to the public and often reserved a year or two in advance.
https://www.nps.gov/grca/planyourvisit/whitewater-rafting.htm