Henry's Fork through Island Park" fetchpriority="high" decoding="async">The Big Springs to Mack's Inn float is a five-mile, two-to-four-hour drift down the headwaters of the Henry's Fork. The water is spring-fed, clear, and 52°F year-round. Self-shuttle starts at the Big Springs day-use area and ends at Mack's Inn. Tubes, kayaks, and canoes all work; outfitters in Mack's Inn rent and shuttle starting around $25 per person.
The classic Island Park float
The Big Springs to Mack’s Inn float on the Henry’s Fork is the canonical Island Park family activity. Five miles, two to three hours, no whitewater, no special skills required. The water is crystal-clear and 52 degrees year-round (it’s spring-fed), the forest is dense on both sides, and wildlife along the route routinely includes moose, bald eagles, trumpeter swans, deer, and big trout visible in the shallows.
From the Mack’s Inn River Adventures TripAdvisor reviews: this is the trip families come back for year after year. The float is closed in winter and shoulder seasons — the official operating window is Memorial Day weekend through Labor Day, with rentals available 9:30 AM to 4:30 PM (Mack’s Inn River Adventures).
How the float works
The route
Put-in: Big Springs Boat Launch — the official boat ramp at Big Springs, where 120 million gallons of water emerge from the ground every day. The water at the ramp is shallow and crystal-clear; it deepens within the first half mile as side springs feed in.
Take-out: Mack’s Inn (4292 US-20), at the north end of Island Park.
Distance: 5 miles.
Time: 2 hours at a steady drift, 3 hours at a typical family pace with swimming stops.
Difficulty: Easy. No rapids. No portages. Slow current, mostly under 2 mph.
Watercraft options
Mack’s Inn River Adventures (the main operator) rents tubes, kayaks, canoes, stand-up paddleboards, and rafts. Tubes are the cheapest and the most casual. Kayaks and canoes give you more control and storage. SUPs work but require basic balance — most floaters who don’t SUP regularly will end up swimming at least once.
Shuttle
Mack’s Inn includes a free shuttle: park at the inn, take their van to Big Springs put-in, float back to your car. If you have your own watercraft, you can run your own shuttle (drop a vehicle at Mack’s Inn first, drive a second to Big Springs), or hire a Mack’s Inn driver to shuttle your own vehicle back — arrange ahead of 5 PM closing.
Cost
2026 pricing varies by watercraft type. Tubes are the lowest tier, SUP/kayak the higher tier. Confirm current pricing at Mack’s Inn River Adventures. Group discounts available for parties of eight or more.
What to bring
Required
- Life jacket (provided with rentals)
- Sun protection (the float runs mostly in shade, but reflective glare on the river still burns)
- Closed-toe water shoes or sturdy sandals (the put-in is gravel and shallow rocks)
- Quick-dry clothing or swimwear
- Towel and dry clothes waiting in the take-out vehicle
Recommended
- Dry bag for phone, keys, snacks (the water is COLD — an unsealed phone is a lost phone)
- Cooler small enough to ride between your legs on a tube or in a kayak hull
- Polarized sunglasses (you’ll see the bottom and the trout more clearly)
- Insect repellent for the put-in/take-out (mosquitoes peak in late June through mid-July)
- Camera or waterproof phone case
Don’t bring
- Glass — the river floor is wadeable and glass breakage is dangerous (and prohibited by most operators)
- Cotton clothing if cold — the water is 52°F. Wet cotton on a windy day gets cold fast
- Anything you can’t afford to lose or that won’t survive submersion
For families with small kids
Children under 5 should be on a parent’s lap in a kayak or canoe rather than on their own tube. Lifejackets must fit. Mack’s Inn carries child-size PFDs but call ahead to confirm availability if you have a toddler.
Other floats in the area
The Big Springs to Mack’s Inn float is the canonical family run. Other options if you want longer days or different water:
Mack’s Inn down to Coffee Pot Rapids (advanced)
The river continues south from Mack’s Inn through more substantial water, including Coffee Pot Rapids — a Class III drop that is NOT a family run. Coffee Pot has injured swimmers and overturned boats. If you continue downstream past Mack’s Inn, take out at the bridge before the rapids unless you have whitewater experience.
Box Canyon (fishing-focused, not a casual float)
Below Island Park Dam, the Box Canyon is a wading-and-fishing destination, not a casual float. Strong current, boulder-strewn bottom, dangerous for non-anglers.
Buffalo River (gentle, less crowded)
The Buffalo River, a Henry’s Fork tributary, has a gentler float that can be combined with fishing for cutthroat. Less developed than the Big Springs run, more solitude.
Lower Henry’s Fork (below Ashton)
Below Mesa Falls and Ashton, the river is different — warmer, slower, more pastoral. Float-fishing-oriented rather than casual tubing.
Where to rent and put in
Mack's Inn River Adventures
The main operator for the Big Springs to Mack's Inn float. Tubes, kayaks, canoes, SUPs, rafts. Shuttle included from the inn to the Big Springs put-in. Open Memorial Day weekend through Labor Day, 9:30 AM to 4:30 PM. Reservations recommended for groups and weekends.
Big Springs Boat Launch
The official put-in for the Big Springs float. A small paved ramp at the head of the Henry's Fork, beside Big Springs National Natural Landmark and Johnny Sack's Cabin. Pit toilets, picnic tables, and parking. No entry fee.
When to go (and when not to)
Best window
Mid-July through mid-August. Warmest air temperatures, longest daylight, fewest mosquitoes (June and early July have the worst bugs at the put-in).
Crowded weekends
Saturday and Sunday in July and August see significant traffic on the river. Float on a weekday for a quieter experience, or float early morning (9:30 AM launch) before the afternoon crowd.
Avoid
- Before Memorial Day weekend: river is too cold and rentals aren’t open
- After Labor Day: rentals close and water temperatures drop fast
- Stormy days: lightning on open water is dangerous; floats are typically suspended during thunderstorms
Where to stay if you're floating
The closest Grandview property to the Big Springs put-in:
- Riverfront Wildlife Lodge — on the Henry's Fork at Big Springs. Walk to the put-in from the property.
For larger groups, the entire collection is within a 15-minute drive of Mack's Inn.
Questions, answered
Is it safe for kids?
Yes. The Big Springs to Mack’s Inn route has no whitewater and slow current throughout. Children should wear properly-sized life jackets and stay in a parent’s lap or a kayak hull rather than on their own tube if under 5.
How long does it actually take?
2 hours at a steady drift. 3 hours at a family pace with swimming and snack stops. Plan for 3.
Can I bring my dog?
Some operators allow dogs on rentals; others don’t. Call Mack’s Inn River Adventures to confirm. Dogs must wear PFDs.
Will I see wildlife?
Almost certainly. Trout in the shallows are routine. Bald eagles are common. Moose and trumpeter swans appear regularly. Bears can be seen at the put-in.
What if it’s a cold day?
The water is 52°F year-round. On a 60°F overcast day with wind, the float will be cold even in a wetsuit. Reschedule if possible.
What if I have my own raft/kayak?
Self-shuttle works (drop a vehicle at Mack’s Inn, drive to Big Springs in a second car), or hire Mack’s Inn to shuttle your vehicle for a fee. The Big Springs put-in is free; no permit required for personal watercraft on this stretch.