Wild weather triggered multiple opening date changes in the last month, with large avalanches damaging the track and covering some sections in debris.
All Great Walks are now open.
Doc's operations director for the Southern South Island, Aaron Fleming, told Midday Report that late spring snow meant there was a high risk of avalanches.
"We couldn't get out to see the damage for some time," Fleming said.
"We couldn't put out staff underneath those avalanche zones so we had to wait for that.
"There was significant damage along the Milford from avalanches coming through, and it was the avalanche risk that was keeping the Kepler and Routeburn closed through those alpine areas."
Doc said early indications showed strong interest in the season ahead, with some tracks already close to capacity on peak dates.
Last season, there were consistently high occupancy across the network, including around 95 percent on the Milford and Abel Tasman tracks.
Fleming said Doc had worked with people who had bookings cancelled to find other options.
"We have had to work very closely with those people who were no doubt very disappointed to not get their slot, but it is always safety first."
