Just an hour from St. Louis, Missouri, Bonne Terre is home to one of the most unique dive sites in the U.S., and possibly the world.

Driving into the sleepy town, it’s hard to imagine that not far beneath the wheels of your car is a billion-gallon underground lake, Bonne Terre Mine. One that you’ll soon be jumping into.

Over the course of a century, miners carved, chipped and drilled their way under Bonne Terre, creating Bonne Terre Mine. At some point during their work they hit water. Miners installed pumps to stop the mine from flooding. Finally, in 1962, they turned the pumps off and the man-made caverns silently filled with crystal-clear water. This preserved the mine and all of its abandoned equipment like a time capsule, and created a one-of-a-kind dive site in the process.

Once a booming town thanks to the mine, Bonne Terre’s history is still on display on its quiet streets. My dive buddy and I stayed at the old train depot-turned-bed and breakfast, owned and operated by the same folks who run the dive shop, West End Diving. It’s quaint, cozy, comfortable and affordable. The next morning, after getting up at Zero Dark Thirty, we drove a mile to the dive shop. It was time for the event that drew us to the area: the annual Bonne Terre Treasure Dive.

The Treasure Dive

The dive works like this: Bonne Terre Mine staff takes a bag of poker chips and scatters them in two different roped-off areas in the mine. The treasure-hungry divers separate into three different groups of about 30 each. At their designated time, they throw themselves in the water, swim to a roped-off area, and scour the bottom for poker chips. Divers only have 10 minutes to find as many chips as they can. Afterward, they swim to another area and do a second hunt. Before leaving the mine, the divers hand their chips to guides, who count them and add them to their account. When each group of divers finishes, guides begin the process over again. At the end of the second round, the divers can use their treasure-hunt findings at an auction that evening to bid on prizes.

Above ground, the atmosphere resembles a Caribbean cookout. People are grilling, eating, drinking (no alcohol until after the second dive, though). The Scuba Cowboy entertains the crowd with music that blends country, rock, and Buffet-style tunes with scuba diving lyrics.

That evening, divers and staff eat together and then go directly to the auction, filled with donated goodies. Everything from two-week trips to exotic locations to wetsuits, drysuit accessories, regulators, and dive computers is up for grabs. Everyone leaves with something, even if it’s just a hat, T-shirt, or key chain.

The day following the hunt, my buddy Anya and I embark on our first real dives in Bonne Terre Mine. We follow the mule trail down into the mine again, glad that our gear awaits us down below from the treasure-hunt dives. We silently dread hauling it back out again when we’re through.

Miners named the mule trail thusly because they used mules to move equipment in and out of the mine. This ¼-mile trail is one of the main reasons the new mine owners were able to turn the mine into a dive site. No need to worry about your tanks though, since the shop requires you to use theirs. Tanks are already at the bottom of the trail, along with weights. Just remember, on your way back up, that excavators carved this trail and all of the mine’s caverns with hand tools.

At the platform, guides are busy filling tanks and directing divers. Water drips from the cavern ceiling, adding to the billion gallons that are already part of the dive site. There’s nothing fancy down here. The dock and surrounding areas are wet and the lighting, though sufficient, is not exactly bright. Aside from tanks filling, all you hear is the dripping water and other divers chatting.

Once you’re geared up, your dive guide — each of whom is a volunteer — gives the go-ahead to get into the water. They’re pretty strict about who gets in the water and when. When you consider that there are 88 square miles of caverns and underwater trails with a maximum depth of over 300 feet, it’s no surprise that they keep a tight rein on the divers. In that vein, guides test all divers for general competency. They’ll want to see you flood and clear your mask and share air with a buddy. Guides will want to ensure that everyone has mastered basic skills before taking them into a semi-dark and occasional overhead environment.

On our first dive we started with Trail No. 1. Divers must progress sequentially through the trails. Keep track of your dives here and ask guides to sign them if you want to do every trail. Guides don’t allow flashes or lights on the first few trails. But you don’t really need them, and their absence keeps divers from venturing off on their own and getting lost.

Despite being lit by more than 500,000 watts, diving in Bonne Terre Mine is somewhat akin to diving at dusk. There are some very dark areas here and there. Photographers won’t be able to get those brightly lit shots. But they will get some amazing silhouettes and haunting images, made all the eerier due to the limited light. In most places divers won’t be able to see the bottom. Instead they’ll be suspended over inky darkness as they glide into swim-throughs and around massive columns of stone. Where the bottom is accessible, divers can see and touch abandoned mining equipment. They can also glimpse parts of mining structures, such as elevators and railways. As you’re swimming around, note that some of the underwater scenes from The Abyss were filmed in these waters. The challenge is figuring out which areas were on the big screen.

The mine is only open to divers on Saturdays and Sundays. As such, if you want to progress through all 28 trails, prepare for several weekend visits.

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