The Jacks Fork is the smaller and faster of the park's two rivers, with high limestone bluffs that close in along long stretches and a sharper gradient than the Current. The classic float is from Blue Spring or Bay Creek down to Alley Spring (8–15 miles depending on put-in), an overnight or a long day depending on pace.
The catch is the water. The Jacks Fork is not as spring-fed as the Current and tends to get bony by mid-July. April and May are the prime months — the river is up, the dogwoods are in flower along the bluffs, and the paddling is fast enough to be interesting. By August you may be dragging your boat over gravel.
Upper Jacks Fork, above Alley Spring, requires a high-water put-in window and some scouting. Below Alley, the river slows down into a more typical float trip into Eminence and on to Two Rivers, where it joins the Current.