Big Springs, First-magnitude spring in Island Park, Idaho, United States

Big Springs is a natural landmark in Island Park that consists of a large spring source producing millions of gallons of clear water daily. The system feeds directly into the Henry's Fork of Snake River and forms one of the region's most significant freshwater sources.

Johnny Sack built the log cabin beside the spring in 1929; it is open to visitors and still holds the mill run by spring water. The spring was designated a National Natural Landmark in August 1980, and the site is managed by the National Forest Service within Caribou-Targhee National Forest.

Rainbow trout gather at the foot of the bridge, where coin-operated dispensers let visitors feed them. The log cabin built by Johnny Sack in 1929 stands beside the spring and is open to visitors; its mill is run by spring water. A caretaker known as Bertha has been known to call out from the cabin window at visitors who leave the marked paths.

A half-mile trail through the site is accessible to wheelchair users and offers viewing of osprey, bald eagles, waterfowl, moose, white-tailed deer and muskrat. Coin-operated dispensers let visitors feed the rainbow trout gathered at the foot of the bridge. Fishing is not allowed until below the outlet to Henry's Lake, several miles away.

Big Springs is the only first-magnitude spring known to issue from rhyolite lava flows, a geology that sets it apart from springs rising from limestone or basalt. The site received National Natural Landmark designation in August 1980 and lies within Caribou-Targhee National Forest, managed by the U.S. Forest Service.