Can You Swim In The Lost Sea?

No — But Here’s What You Can Do

No, you cannot swim in the Lost Sea. Swimming, wading, and fishing are all prohibited. The Lost Sea is a protected underground lake inside Craighead Caverns, 140 feet below the surface, and public access is limited to guided walking tours that end with a glass-bottom boat ride across the lake. You can trail your hand in the water from the boat — it’s a constant 58°F — but that’s as close to “swimming” as it gets. The restriction exists to protect both the cave environment and visitors; the water is cold, the lake floor drops to roughly 70 feet in places, and the cave system extends into unmapped underwater passages that even experienced cave divers have not fully explored.

What Is the Lost Sea?

The Lost Sea is America’s largest underground lake and the second-largest non-subglacial underground lake in the world (after Dragon’s Breath Cave in Namibia). It sits inside Craighead Caverns, a large cave system in Monroe County, Tennessee, between the towns of Sweetwater and Madisonville — about 50 miles south of Knoxville in the foothills of the Great Smoky Mountains. The visible surface of the lake measures approximately 800 feet long and 220 feet wide, covering about 4.5 acres. But that’s only the mapped portion. Cave divers have explored additional rooms completely filled with water — more than 13 acres of submerged passages have been charted — without reaching the end. The full extent of the Lost Sea remains unknown.

The lake was designated a National Natural Landmark by the National Park Service in 1974. The cave system is also known for its rare anthodites — delicate, spiky crystal formations commonly called “cave flowers” — found in only a handful of caves worldwide.

History of the Caverns

Craighead Caverns have been used by humans for centuries. Cherokee artifacts — pottery, arrowheads, weapons, and jewelry — have been found nearly a mile from the entrance in a chamber now called the Council Room. The caverns are named for Chief Craighead, who held ownership of the land in the early 1800s.

European settlers discovered the cave system around the 1820s and used the constant 58°F temperature as natural refrigeration for storing food. During the Civil War, Confederate soldiers mined saltpeter from the caverns for gunpowder production — authentic 1863 graffiti has been carbon-dated inside the cave. In the early 1900s, one chamber was converted into a dance hall, and moonshiners used the underground system to produce illegal spirits out of sight. A functioning moonshine still from that era is still on display along the tour route.

The lake itself was discovered in 1905 by Ben Sands, a 13-year-old boy who crawled through a small muddy opening deep inside the cave and dropped into a chamber so large he couldn’t see its edges by lantern light. He threw mudballs into the darkness and heard only splashes. By the time he brought his father back to see it, rising water had hidden the entrance, and the lake wasn’t rediscovered for several more years. In 1939, cave guides exploring during off-hours found the fossilized remains of a Pleistocene jaguar — an animal that apparently wandered into the cave roughly 20,000 years ago, became lost in the darkness, and eventually fell into a crevice. Jaguar bones and footprint casts are now held by the American Museum of Natural History in New York.

Visiting the Lost Sea: Tour Details

The Lost Sea Adventure is the only way to see the lake. Tours are guided and run daily year-round (closed Thanksgiving and Christmas Day). Here’s what to expect:

The walk in: The tour begins with a three-quarter-mile round-trip walk on a sloping path down into the caverns. The descent is gradual but steady — you’re going 140 feet underground. Along the way, your guide covers the cave’s history, points out geological formations, the moonshine still, Civil War-era graffiti, and the anthodite crystal displays. The walk to the lake takes about 20 to 25 minutes.

The boat ride: At the bottom, you board a glass-bottom boat for a ride across the lake. Colored lighting illuminates the water and cave walls. Rainbow trout swim in the clear water below the boat — they were introduced and are maintained for the visual interest of tour visitors (fishing is not permitted). The boat ride lasts about 20 minutes.

The walk back: The return is uphill on the same path. The 140-foot climb is the most physically demanding part of the tour — it’s not strenuous for most people, but it’s worth knowing if you have mobility concerns. The total tour time is approximately 1 hour and 15 minutes.

Temperature: The cave maintains a constant 58°F year-round. Bring a light jacket or long sleeves even in summer — it feels cool after the Tennessee heat outside.

Hours: Seasonal hours vary. Summer (May–August): 9 a.m. to 7 p.m. Spring/Fall (March–April, September–October): 9 a.m. to 6 p.m. Winter (November–February): 9 a.m. to 5 p.m.

Prices: Adults (13+) $24.95; children (4–12) $14.95; children 3 and under free. Wild Cave Tours (a more adventurous option involving crawling and off-trail exploration) are also available at higher prices.

Above Ground

The Lost Sea Adventure complex includes a gift shop and a small heritage village near the parking area with a blacksmith shop, general store, sweet shop, and a glass-blowing demonstration studio. A gem mining sluice is available for kids. These are modest commercial additions, but the glass-blowing is genuinely interesting and the gem mining keeps younger children entertained while adults browse.

Getting There

The Lost Sea is located at 140 Lost Sea Road, Sweetwater, Tennessee 37874 — a short drive off New Highway 68 between Sweetwater and Madisonville. From Knoxville, take I-75 South to exit 60 (TN-68 toward Sweetwater), then follow TN-68 South for about 7.5 miles to Lost Sea Road. The drive from Knoxville is about 50 minutes. From Chattanooga, take I-75 North to the same exit — about 90 minutes.

For more Tennessee cave experiences, see our guide to what to wear to the Lost Sea. If you’re exploring the broader Smoky Mountains area, check out our guides to downtown Gatlinburg attractions and romantic things to do in Pigeon Forge.