You might know the phrase “half the park is after dark,” a National Park Service campaign designed to spread out visitors and encourage them to explore in new ways. But to avoid the crowds in the country’s most beloved places, going out under the moonlight isn’t the only option for seclusion—you can go underwater.

And it’s not just the nation’s coastal parks that offer watery worlds to explore. From the bubbles of Yellowstone to the shipwrecks of Isle Royale, the parks below offer uncommon, unparalleled experiences—where the only crowds come with fins, flippers, and gills. Just make sure you check with each park on permits and other guidelines before you go, so you're well prepared.

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While daily crowds around Yellowstone’s epic geysers and hot springs number in the tens of thousands, that’s on land. Naturally, Yellowstone Lake, one of the world’s largest alpine lakes, has geothermal features of its own.

In the lake’s northeast corner, skilled divers can swim through the “champagne” of Mary Bay, where hot bubbles vent from the algae-covered lake bottom like fizz, their heat distorting the water’s visibility. The West Thumb of the lake—next to the hikeable West Thumb Geyser Basin—is even wilder: Here, underwater vents erupt and surge like a submerged version of Old Faithful. Even expert divers should defer to Mother Nature and take caution.

Rolling from rocky beaches and mossy rainforests up to wintry mountain peaks, Olympic National Park isn’t exactly shy on spectacular experiences, including swimming and diving.

Instead of heading for the Pacific, hit the clear waters of Lake Crescent, right off Highway 101. Visibility often exceeds 150 feet here (Crater Lake, famous for its exceptionally pristine waters, averages around 100 feet). Sledgehammer Point is a great spot for a dive, where sheer walls tempt divers into the abyss; at 600-plus-feet, Lake Crescent is also staggeringly deep. 

For swimmers, East Beach offers easy, kid-friendly splashing, and Devil’s Punchbowl, a bridge-lined cove about a mile down the Spruce Railroad Trail, has more than a few rocky spots to jump into these deep blue waters. 

Note: Swim by day, kayak by night. The waters bordering the park, including the Salish Sea and the Hood Canal, are bioluminescent.

An island wilderness, Isle Royale National Park sits in the treacherous waters of Lake Superior, where it’s seen its fair share of shipwrecks. These cold, fresh waters preserve one of the most intact collections of shipwrecks, like a submerged museum of America’s maritime history.

Ten major shipwrecks lie within the park's boundaries, from vintage wooden steamers to steel freighters, some still displaying original paint, machinery nameplates, and cargo. The most popular to dive is the S.S. America, a 1928 package freighter that’s remarkably intact, submerged only eight feet at its highest point, and accessible from Windigo, the park’s western hub. Book a charter out of Grand Portage, Minnesota, and be prepared for chilly waters that drop to 34°F.

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Just south of Miami, Biscayne National Park protects the northernmost living coral reef in the United States. With 95 percent of the park submerged, there’s little to do here but enjoy the water and its diverse marine life—which includes over 600 native fish species, as well as sea turtles, manatees, and dolphins.

Even snorkelers staying in clear, shallow waters can get up close to gentle sharks, jellyfish, lobsters, moray eels, and a whole rainbow of fish. While the 25-mile-long coral reef is certainly the park’s star attraction, snorkelers can also wander the fringes of mangroves and get an arm’s length from shipwrecks.

Divers have an even wider world to explore. Sponge Fantasy, where giant basket sponges pop out, keep the imagination busy; and the Maritime Heritage Trail and its six shipwrecks, from the 1870s to the 1960s, ground divers in history. Whatever world you choose, when you come up for air, you’ll get a strange splash of reality: Miami’s modern skyline rises just beyond the water.

Swimming and snorkeling are prohibited in Missouri’s gorgeous springs, but the rivers they sprout are fair game. Here on the Ozark Scenic Riverways and the Buffalo National River, it’s not about wild coral reefs or shipwrecks—it’s the chance to drift gently with the current, floating underneath massive forest-topped bluffs and keeping company with sunfish and turtles. 

Autumn is the prime time for swimming, tubing, kayaking, and snorkeling here, as the water levels are ideal, temperatures are comfortable, and the Ozarks spark with fall foliage. The rivers have tannic but not cloudy waters, with visibility typically ranging from 10–20 feet. There are many access points along both the Current and Buffalo rivers, making it easy to get in and out of the water at your leisure, and area campgrounds—like Steel Creek Campground—are plentiful, too. Many visitors combine snorkeling with canoeing, kayaking, or inner-tubing for a full day of river exploration.

Nicknamed "North America's Galapagos," Channel Islands National Park protects five islands and the surrounding marine ecosystem off the coast of Southern California. Just a few hours from the glitter of Los Angeles, the park represents a more ancient California, one of the few pristine marine environments left on the West Coast.

The kelp forests around the Channel Islands are among the park's most spectacular underwater worlds. While that may sound underwhelming to dive, it’s quite the opposite; picture floating through a forest sans gravity, rays of sun dancing between the kelp strands. It’s a vertical, three-dimensional habitat teeming with colorful Garibaldi fish, basking sharks, octopus, sea lions, and harbor seals making cameos. 

Water-seekers typically concentrate around Santa Barbara and Anacapa islands, as those typically offer the warmest, calmest waters. Gull Island, off of Santa Cruz Island, is a great spot for both snorkeling and diving, too—at least for those not afraid of a few wildlife encounters.

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