All vessels coming in from sea to the Atchafalaya bay, for the purpose of receiving cargo, shall take a pilot on board when he offers his services outside of the reefs.  The pilot shall examine whether the vessel has any ballast on board, and when ballast is found, the vessel shall be conducted by said pilot to the place selected for the discharging of ballast, where the captain or master of said vessel must discharge his ballast; if the vessel has no ballast on board she shall be conducted by the pilot to the usual anchorage.