A floating assemblage of tree trunks, branches, bark, leaves, root wads, and litter that comes together in a river’s flow goes under the collective name raft. Rafts ride the current until they break up, waterlog, and sink, or until they make landfall. For a mass of driftwood in the water, such as the great rafts that come down the Yukon after spring breakup, Koyukon Athabaskan say neetohudaaneeltzaakk. When a river undercuts its banks, sweeping tangled masses of vegetation out to sea, animals may go along for the ride. Rafts can bridge oceanic barriers, explaining cases of species disjuncture, whereby plants or animals occur in locations isolated from their main range. Log booms are the human-assembled, commercial equivalent. Benson rafts (or cigar rafts) were huge, elliptical booms up to fifty-five feet wide, thirty-five feet high, and a thousand feet long, cabled tight for towing downcoast to San Francisco. Flat booms are still pulled by tugs on the Columbia River, whose dams prevent rafts of natural debris from reaching the Pacific, depriving pelagic fish and their ecosystem of a vital source of nutrients and shelter.

Robert Michael Pyle