The Spring River is Arkansas's spring-fed alternative to the big White-system tailwaters — a constant, cold river born whole at Mammoth Spring on the Missouri line, where one of the country's great springs pushes out enough water to make a river in a single bound. Below the old dam at Mammoth Spring State Park it runs about a dozen miles of ledges, rapids and gravel runs as a stocked rainbow fishery with browns and the odd cutthroat, popular with canoes and families and fly fishers alike. Because the cold comes from the spring rather than a reservoir release, it fishes stable and cold year-round and doesn't pulse with generation — a friendlier, more predictable river than the White. Fish scuds, midges and soft hackles, work the ledges and pocket water, and share it gracefully with the float traffic in summer.

• Limestone