The Collaborative International Dictionary of English v.0.48:

Waterway \Wa"ter*way`\, n. (Naut.)
   Heavy plank or timber extending fore and aft the whole length
   of a vessel's deck at the line of junction with the sides,
   forming a channel to the scuppers, which are cut through it.
   In iron vessels the waterway is variously constructed.
   [1913 Webster]

WordNet (r) 3.0 (2006):

waterway
    n 1: a navigable body of water
    2: a conduit through which water flows [syn: watercourse,
       waterway]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "waterway":
   adolescent stream, approaches, aqueduct, arroyo, beck, bed, bourn,
   braided stream, branch, brook, brooklet, burn, canal, channel,
   creek, creek bed, crick, culvert, donga, dry bed, fairway,
   flowing stream, flume, fluviation, fresh, freshet, gill, gulch,
   gully, gullyhole, headrace, irrigation ditch, kill, lazy stream,
   meandering stream, midchannel, midstream, millstream, moving road,
   navigable river, nullah, race, racing stream, river, river bed,
   riverway, rivulet, road, run, rundle, runlet, runnel, sea lane,
   seaway, ship route, sike, sluice, spill stream, spillbox, spillway,
   steamer track, stream, stream action, stream bed, streamlet,
   streamway, subterranean river, swash, swash channel, tailrace,
   wadi, water carrier, water channel, water furrow, water gap,
   water gate, watercourse, waterworks