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]