It's true that many of the world's most coveted scuba diving and snorkeling destinations are located outside of the U.S. However, there are plenty of underwater spots Americans can visit without the benefit of a passport. Consider one of these 20 places.

Monterey Bay attracts tens of thousands of divers each year as the national marine sanctuary here features ideal visibility as well as safe conditions. Nonetheless, visiting divers will want to pack a wetsuit as the water can be quite chilly at times.

A premier destination for snorkelers and divers, the Florida Keys is home to the Diving Capital of the World in Key Largo. This beautiful island chain also boasts North America's only living coral reef in addition to numerous diving shops, instructors and tour operators ready to ensure a once-in-a-lifetime underwater experience.

A healthy marine environment helps set California's Catalina Island apart from some of the country's other popular diving spots as curious snorkelers and scuba divers will enjoy tremendous visibility allowing them to take in more colorful sea life than they ever thought possible.

Big Island Divers has you covered when it comes to diving and snorkeling experiences from Kona, including daytime scuba dive charters, nighttime reef dives and unforgettable snorkeling excursions to see dolphins, Manta rays and much more.

Scuba divers taking the plunge in Morehead City, North Carolina can come face to face with the spectacular sand tiger shark. In fact, it's one of the few places in the country where you can swim with sharks safely.

You won't need a passport to go diving near Bellingham, which is about 90 minutes north of Seattle just east of Washington's San Juan Islands. Local scuba instructors make it easy to learn the ropes to explore below the surface of the Pacific Northwest.

Alaska's Baranof Island is home to the country's second-largest city by land area in Sitka. Visitors to this region of the Last Frontier will find exceptional diving opportunities, including rocky reefs and stunning kelp gardens.

The Downtown Aquarium in Denver offers a plethora of underwater adventures, including a once-in-a-lifetime shark cage experience for ages eight and up that doesn't even require diving certification as an A-1 Scuba & Travel Aquatics Center dive guide will assist you every step of the way.

Divers looking to explore one of the world's best collection of shipwrecks can't go wrong in Thunder Bay. The Joseph S. Fay and the William P. Rend are among some of the National Marine Sanctuary's most coveted wrecks.

Port Deco Divers make scuba diving in Lake Michigan off of Port Washington, Wisconsin-about 25 miles north of Milwaukee-easy and fun as they offer helpful scuba training for beginners and charters for certified divers.

Some of the best snorkeling and diving in the Sunshine State can be found 90 minutes north of Tampa in Crystal River, which is the only place in the U.S. where you can legally swim with manatees.

Visitors to San Diego won't want to pass up an opportunity to go scuba diving in La Jolla. The protected marine sanctuary here provides divers with thrilling up-close encounters with seals, octopus and even eye-popping leopard sharks.

Elsewhere in Hawaii, Kauai boasts some of the world's most diverse marine life. Experienced divers who haven't been yet should add the Garden Island to their bucket list as they'll have a chance to spot the endangered Hawaiian green sea turtle, schools of colorful fish and a whole lot more.

Located on Puerto Rico's western coast in the Tres Palmas Marine Reserve, Steps Beach is unique in that it's among the few places in the U.S. territory where visitors can snorkel from shore. Plan your trip between April and August to take advantage of calmer waters.

Like Puerto Rico, American citizens don't need a passport in order to experience the U.S. Virgin Islands of St. Croix, St. John and St. Thomas. Even beginners will love Trunk Bay as the Underwater Trail here makes it incredibly easy to experience mesmerizing coral and fish up close.

Scuba diving and snorkeling in Florida isn't limited to the Keys. The Emerald Coast comprising Destin, Okaloosa Island and Ft. Walton Beach offers miles of vibrant waters that divers can explore with the help of Emerald Coast Scuba and Destin Snorkel.

Similar to Denver, visitors to Atlanta can dive alongside majestic marine creatures at the Georgia Aquarium. The attraction's Journey with Gentle Giants program is the only opportunity in the world where you're guaranteed to dive with whale sharks. Guests will have the help of a trainer, spend as many as 30 minutes in the water and even take home a souvenir photo and t-shirt.

A diver's paradise, Maui boasts a handful of can't-miss underwater sites, including the Lanai Cathedrals, which are caverns 50 feet deep comprising a wide variety of marine life ranging from sharks and dolphins to turtles and so much more.

Visitors to New England will be drawn to the stunning plant and animal life that lurks below the surface near Cape Neddick in York, Maine. This is also one of the most picturesque diving sites in America thanks to the iconic Nubble Lighthouse.

Oahu is the place to interact with a slew of magnificent marine animal species, including the rare Hawaiian monk seal. First time diving? Oahu Diving excels at providing beginners with an unforgettable underwater journey.