The Collaborative International Dictionary of English v.0.48:

Conservancy \Con*serv"an*cy\, n.
   Conservation, as from injury, defilement, or irregular use.
   [1913 Webster]

         [An act was] passed in 1866, for vesting in the
         Conservators of the River Thames the conservancy of the
         Thames and Isis.                         --Mozley & W.
   [1913 Webster]

WordNet (r) 3.0 (2006):

conservancy
    n 1: a commission with jurisdiction over fisheries and
         navigation in a port or river
    2: the official conservation of trees and soil and rivers etc.