The Henrys Fork is not one fishery — it's a chain of very different reaches running from the cold spring sources at the top, down through the Island Park tailwater and Box Canyon, across the famous Harriman flats, into the Mesa Falls canyon and on to the easier lower river around Ashton. Most of it is public water fished on an Idaho license, but public water does not mean public bank access: a lot of the frontage is private, so plan to get in through official access points, public land, state-park access, or a guide. Special regulations and seasons change reach by reach — most notably Harriman State Park, which is closed December 1 through June 14. And it's a tailwater: warm, turbid water released from Island Park Reservoir in a low-water summer can flatten the fishing in Box Canyon and on the Ranch even when the hatch chart says otherwise. Always check current Idaho Fish & Game regulations before you fish.