National marine sanctuaries are marine protected areas that preserve some of the most iconic and ecologically significant marine environments in the United States, from vibrant coral reefs to historic shipwreck sites. Snorkeling at these underwater parks offers a uniquely immersive experience, allowing visitors to explore thriving aquatic ecosystems, encounter a diverse array of marine life, and even swim above centuries-old shipwrecks. These protected waters offer not only natural beauty but also a deep connection to the cultural and historical stories that define America’s coastal legacy.
1. Shipwrecks
America’s national marine sanctuaries offer one-of-a-kind snorkeling adventures where history and marine life come together beneath the surface. In Florida Keys National Marine Sanctuary, the Shipwreck Trail invites snorkelers to explore centuries-old wrecks resting in shallow tropical waters, many less than 25 feet deep. Highlights include the wreck of San Pedro, a 1733 Spanish treasure fleet ship, and North America, a three-masted vessel from the early 1800s, both surrounded by vibrant coral and fish. The shipwreck Adelaide Baker, about 20 feet deep near Duck Key, and the well-known Benwood, a WWII-era freighter, are not only rich in history but also thriving artificial reefs teeming with marine life.
Similarly, Wisconsin Shipwreck Coast National Marine Sanctuary offers an equally compelling snorkeling experience in a shallow, clear, freshwater environment. Dozens of 19th-century wrecks, like Continental, Lasalle, Lookout, and Atlanta, rest in just 5 to 17 feet of water, often close to shore and perfect for beginning snorkelers or families. These well-preserved wooden vessels tell stories of Great Lakes commerce, storms, and shipbuilding innovation, all visible just below the surface. Further north, in Thunder Bay National Marine Sanctuary in Lake Huron, cold freshwater has preserved over 100 shipwrecks with some visible right from the surface. Snorkelers can explore wooden steam barges like D.M. Wilson and Monohansett, as well as dramatic collision sites like Defiance and John L. Hackley, all in 20 feet of water or less. The stillness of the lake and the clarity of the water make it feel like swimming through a historical museum frozen in time.
On the Pacific coast, Channel Islands National Marine Sanctuary offers a spectacular fusion of rich marine biodiversity and underwater cultural heritage, making it a unique destination for snorkelers seeking both natural beauty and historical intrigue. While many of the sanctuary’s shipwrecks lie in deeper waters suited for divers, several notable wrecks are accessible to confident snorkelers under the right conditions. One such site is Aggi, a three-masted sailing ship that sank near Santa Rosa Island and now rests in 20 to 50 feet of water. Parts of the wreck are visible in the shallower range, especially when seas are calm, and are surrounded by dense kelp forests teeming with life. Another highlight is the USS Cuba, a steamship that went down off San Miguel Island in 1923. Though located in a more dynamic environment, scattered sections of the wreck can be explored by experienced snorkelers when visibility and conditions allow. Also noteworthy is the wreck of Winfield Scott, a Gold Rush-era paddle steamer that lies under about 25 feet of water off Anacapa Island. While currents can be strong at times, its relatively shallow depth offers opportunities for exploration.
2. Kelp Forests
The kelp forests of Channel Islands National Marine Sanctuary and Monterey Bay National Marine Sanctuary provide an astounding snorkeling journey into two of the ocean’s most vital and ecologically rich environments. These towering forests of giant kelp (Macrocystis pyrifera), can grow up to 2 feet per day and reach lengths of 150 feet—forming dense, swaying canopies that resemble underwater cathedrals. In the Channel Islands, crystal-clear waters reveal a lively world where sea lions dart between fronds, garibaldi fish glow like embers, and golden sunlight dances across the reef below. Meanwhile, Monterey Bay’s kelp forests offer encounters with sea otters cracking shellfish on their chests, harbor seals weaving silently through the kelp, and schools of rockfish sheltering in the layered foliage. These forests are among the most biodiverse ecosystems on Earth, providing food, shelter, and nursery grounds for countless species, including commercially important fish. They also serve vital ecological roles, buffering shorelines from storms, sequestering carbon, and supporting the health of entire marine food webs. Snorkeling in these kelp forests is not just an incredible experience; it’s a powerful reminder of the beauty, complexity, and urgency of safeguarding our ocean’s most essential habitats.
3. Coral Reefs
Though coral reefs cover less than 1% of Earth’s surface, they support over 25% of all marine life, making these ecosystems true underwater powerhouses. National marine sanctuaries in the Florida Keys, Hawaiian Islands, and American Samoa offer an unforgettable journey snorkeling through some of the most vibrant and biologically rich marine coral reef environments in America. In Florida Keys National Marine Sanctuary, home to the only living coral barrier reef in the continental U.S., snorkelers can drift above shallow coral gardens teeming with sea turtles, parrotfish, stingrays, and eels. With over 700,000 snorkelers and divers visiting each year, the sanctuary offers easy access to breathtaking underwater landscapes, from reef flats to historical shipwrecks. In the last 40 years, healthy coral cover on the reefs within Florida Keys National Marine Sanctuary has declined more than 90%. This decline can't be blamed on a single cause, but rather a web of interconnected problems. Divers and snorkelers can participate in a unique opportunity to help out through the Iconic Reef Guardians program, a first-of-its-kind calling to restore the health of coral reefs in the Florida Keys for future generations.
In Hawaiian Islands Humpback Whale National Marine Sanctuary, coral reefs thrive beneath volcanic shorelines, supporting creatures like green sea turtles, moray eels, octopuses, and the strikingly colorful reef fish featured in NOAA’s "Hawaiian Reef Creatures" video. These reefs are not only a visual wonder but also a critical part of koholā (humpback whales') seasonal habitat, as they return each winter to give birth and nurse their young in these warm, sheltered waters.
Meanwhile, National Marine Sanctuary of American Samoa boasts some of the most pristine and diverse coral reefs in the world. Snorkelers here can explore reef slopes bursting with over 1,000 species of fish and invertebrates, massive table corals, and ancient Porites coral heads, one measuring over 23 feet tall and 135 feet around. Giant clams, or faisua, with their brilliantly colored mantles, add to the reef's spectacle and serve as keystone species vital to reef health.
4. Sponges
The National Marine Sanctuary System offers a special snorkeling opportunity to discover one of the ocean’s most intriguing yet frequently overlooked organisms: marine sponges. These animals, anchored to the seafloor and reef, not only support water clarity and biodiversity, but also offer snorkelers an unforgettable view of one of our planet’s most fascinating and ancient inhabitants.
In Florida Keys National Marine Sanctuary, vibrant sponge gardens flourish alongside coral reefs and seagrass beds, filtering thousands of gallons of water each day and creating vital habitat for marine life. Among them, the giant barrel sponge (Xestospongia muta), often called the "redwood of the reef", is the largest sponge species in the western Atlantic Ocean, growing up to 6 feet tall and wide. These massive sponges are like underwater apartment complexes, with animals like shrimp, crabs, nudibranchs, pufferfish, cardinalfish, and even spiny lobsters living within them.
In Channel Islands National Marine Sanctuary and Monterey Bay National Marine Sanctuaries off California’s coast, cold-water sponges, including colorful encrusting and vase varieties, cling to rocky reefs and kelp forest outcroppings, adding both texture and ecological function to these rich underwater landscapes. Over in Hawaiian Islands Humpback Whale National Marine Sanctuary, sponges can be found nestled among coral reefs, contributing to reef health while offering refuge and food to reef-dwelling organisms. Sponges also offer entertainment on occasions to spinner dolphins who sometimes use them as a play toy!
In Gray’s Reef National Marine Sanctuary off Georgia’s coast, sponges are vital to the live-bottom habitat, forming a colorful mosaic across rocky ledges. These sessile invertebrates filter water, recycle nutrients, and provide shelter for a wide range of marine species. Located between temperate and tropical waters, the sanctuary supports a mix of biodiversity, resulting in a unique sponge fauna.
5. Giant Clams
Snorkeling in National Marine Sanctuary of American Samoa offers a rare and extraordinary opportunity to witness one of the ocean’s most captivating inhabitants, giant clams, known locally as faisua. These incredible mollusks, specifically Tridacna maxima, Tridacna noae, and Tridacna squamosa, are more than just beautiful reef dwellers. With their colorful, iridescent mantles and sheer size, they create a visually striking experience for snorkelers gliding through the sanctuary’s clear, shallow waters. Giant clams are ecological powerhouses.
As keystone species, they play a critical role in maintaining the health and stability of coral reef ecosystems. They form a symbiotic relationship with zooxanthellae, photosynthetic algae that live inside their tissues. These algae provide essential nutrients to the clam via sunlight, while the clam offers the algae a safe habitat and access to light. This relationship not only sustains the clams but also gives them their vivid hues, which ripple with blues, greens, and purples in the sunlight, making them mesmerizing to observe up close. The sanctuary’s warm, sunlit reef flats are perfect for supporting giant clams and their symbionts, and snorkeling among them offers a peaceful way to experience the abundance of American Samoa’s marine biodiversity. Seeing faisua in their natural environment is not just breathtaking, it’s a meaningful reminder of what we stand to lose without continued protection of these unique marine sanctuaries.
6. Seagrass Meadows
Exploring the vibrant seagrass meadows and thriving underwater ecosystems of Florida Keys National Marine Sanctuary, Hawaiian Islands Humpback Whale National Marine Sanctuary, and National Marine Sanctuary of American Samoa offers a magical journey beneath the waves. In Florida Keys National Marine Sanctuary, over a million acres of vast emerald carpets of seagrass habitat provide critical nursery areas for juvenile fish and serve as feeding grounds for sea turtles and manatees. These meadows also play an integral role in maintaining water quality by trapping sediments and nutrients before they reach coral reefs, as well as creating shimmering fields that filter sunlight and invite exploration through their dappled, dreamlike glow.
In Channel Islands National Marine Sanctuary, delicate beds of eelgrass sway in the currents of sheltered coves, providing refuge for juvenile fish, invertebrates, and foraging seabirds. These underwater meadows knit together the sanctuary’s diverse habitats, linking kelp forests, rocky reefs, and sandy bottoms while stabilizing sediments and filtering the water. Though smaller and patchier than the vast seagrass expanses of the Florida Keys, the sanctuary’s eelgrass beds are vital pockets of productivity that invite quiet exploration for those who venture beneath the surface.
Together, these sanctuaries offer snorkelers an immersive glimpse into some of the ocean’s most bountiful environments on the planet, where every blade of seagrass breathes life into the marine world.
7. Sea Turtles
Gliding through sun-drenched tropical seagrass beds, volcanic coastlines, temperate waters, and nutrient-rich upwellings, many national marine sanctuaries offer snorkelers an extraordinary opportunity to witness sea turtles. In Florida Keys National Marine Sanctuary, green and loggerhead sea turtles peacefully graze on expansive seagrass meadows, vital for maintaining water clarity and sediment stability, while hawksbill turtles forage in the crevices of coral reefs for sponges to eat.
Thousands of miles away, Hawaiian Islands Humpback Whale National Marine Sanctuary provides a dramatic setting where snorkelers can encounter honu (green sea turtles), that glide gracefully near lava rock coastlines and coral heads, carrying profound cultural significance as ancestral guardians. In the pristine coral atolls of National Marine Sanctuary of American Samoa, green and critically endangered hawksbill turtles forage among vibrant reef formations, revealing one of the most untouched turtle habitats in the Pacific.
Meanwhile, loggerhead, green, and leatherback sea turtles use Gray’s Reef National Marine Sanctuary off Georgia’s coast as habitat, with its sandstone ledges and sponge-covered ridges. On the West Coast, California’s Channel Islands, Chumash Heritage, and Monterey Bay national marine sanctuaries serve as feeding grounds for transient turtles like the olive ridley and Pacific leatherback, especially during warm water incursions and seasonal upwelling events.
Snorkeling alongside these ancient, graceful reptiles offers not only unforgettable encounters but also a profound reminder of the interconnectedness of ocean life and our shared responsibility to protect these vital habitats for future generations to enjoy. Remember to give wildlife their space, and follow our Wildlife Viewing Guidelines.
8. Schooling and Shoaling Fish
Within America’s national marine sanctuaries, snorkelers can witness a stunning diversity of schooling and shoaling fish, each uniquely adapted to thrive in its specific environment. In Florida Keys National Marine Sanctuary, snorkelers are treated to dazzling schools of sergeant majors that dart among coral heads while grunts and snappers often gather in large, motion-synchronized groups under reef overhangs. Jacks, known for their speed and power, cruise the reef edges in tight formation, frequently hunting in coordinated bursts. Meanwhile, Gray’s Reef National Marine Sanctuary off Georgia hosts schools of Atlantic spadefish, as well as Atlantic menhaden, vital for filtering plankton from the water and supporting a wide range of marine life.
In Hawaiian Islands Humpback Whale National Marine Sanctuary, tropical schools of goatfish sift through sandy bottoms with their whisker-like barbels, while parrotfish and surgeonfish graze reef algae in colorful clusters, playing a key role in reef health.
Channel Islands National Marine Sanctuary offers a temperate contrast, with over 400 species of fish having been documented in the sanctuary. Snorkelers might witness massive, shimmering schools of Pacific sardines or anchovies moving in unison through kelp forests, pursued by predators like jack mackerel. In Monterey Bay National Marine Sanctuary, schools of blue rockfish can be seen swimming in kelp forests, and large schools of northern anchovy and herring provide critical food sources for marine mammals and seabirds, forming bait balls and feeding frenzies that can be awe-inspiring to observe.
In National Marine Sanctuary of American Samoa, pelagic schools of blackfin barracuda and Pacific yellowfin tuna cruise the blue ocean, while parrotfish add bursts of color to volcanic reefs, often mixing with jacks and bigeye scad in impressive swarms. Over 990 species of fish have been documented in Samoan waters—a remarkable level of biodiversity.
Even in freshwater sanctuaries like Thunder Bay National Marine Sanctuary and Wisconsin Shipwreck Coast National Marine Sanctuary, snorkelers can spot schooling cisco, smelt, and alewife gliding over historic shipwrecks. These fish are key forage species in the Great Lakes, their silvery schools a shimmering part of the ecosystem’s foundation. Whether tropical or temperate, saltwater or freshwater, each sanctuary offers a chance to witness the coordinated beauty and ecological importance of schooling fish.
9. Nudibranchs
While snorkeling among the coral gardens and kelp forests of your national marine sanctuaries, you might encounter one of the ocean’s most vibrant and mesmerizing creatures—the nudibranch. These soft-bodied sea slugs are living jewels, dressed in electric blues, fiery oranges, and dazzling purples, with delicate frills and feathery appendages that flutter as they glide across reefs and rocks. In Florida Keys National Marine Sanctuary, lettuce sea slugs (Elysia crispata) can often be spotted near coral heads and sponge-covered outcroppings.
Along the chilly, kelp-draped coasts of California’s Channel Islands National Marine Sanctuary and Monterey Bay National Marine Sanctuary, divers and snorkelers may find surreal species like the Spanish shawl (Flabellinopsis iodinea), whose glowing purple body and orange cerata make it one of the Pacific’s most iconic invertebrates, or the translucent white-lined Dirona, which seems to hover like a ghost through the swaying kelp.
In Hawaiian Islands Humpback Whale National Marine Sanctuary, keen-eyed snorkelers sometimes discover dorid sea slugs in the Goniobranchus genus inching across lava flows and reef rubble, while larger species, such as the Hawaiian yellow margined spanish dancer (Hexabranchus aureomarginatus) will dazzle snorkelers exploring the shallow reefs and rocky crevices around Oahu.. National Marine Sanctuary of American Samoa, nestled in a hotspot of Pacific biodiversity, is thought to harbor many rare and endemic nudibranchs, still being described by science, thanks to its lush coral habitats.
In the sandier Gray’s Reef National Marine Sanctuary on the East Coast, wherenudibranchsare more elusive, observant snorkelers may be rewarded with sightings of the blue and yellow regal sea goddess nudibranch (Felimare picta), hiding among sponges or hard-bottom ledges. From sunlit tropical shallows to misty kelp forests, these radiant sea slugs are tiny wonders—living, breathing works of art that reflect the incredible ecological richness protected by NOAA’s national marine sanctuaries.
10. Underwater Natural Landmarks
More than just a chance to see vibrant marine life, exploring America’s national marine sanctuaries through snorkeling unveils a world of dramatic underwater landscapes shaped by ancient geology and thriving ecosystems. In Florida Keys National Marine Sanctuary, snorkelers can glide over a seascape shaped by time and tides, where ancient coral reefs and sandbars have become solid rock. The sanctuary’s seafloor is built from Key Largo and Miami Limestone, remnants of prehistoric coral formations exposed and hardened during past ice ages when sea levels dropped dramatically. These underwater limestone structures have since been sculpted into coral pinnacles, ledges, and small arches, creating natural swim-throughs and hiding places for marine life. Not only do these porous formations support vibrant ecosystems, but they also influence water quality, as they allow water and nutrients to flow between land and sea, shaping both the physical and biological character of the reef.
In Channel Islands National Marine Sanctuary, the seafloor is even more dramatic and diverse than the islands above, offering an underwater landscape sculpted by time and tectonics. Snorkelers can explore a range of striking features, from rocky reefs and broad sandy flats to ancient submerged shoreline terraces and sea caves. Towering pinnacles and sea arches rise from the ocean floor, while just beyond the islands, the Santa Cruz Basin plunges to depths of over a mile, which is deeper than the Grand Canyon itself. These dramatic geological formations create habitats for rich marine life and provide snorkelers with an awe-inspiring sense of scale and exploration beneath the surface.
In Monterey Bay National Marine Sanctuary, snorkelers are immersed in one of North America's most dynamic marine environments, where geological features and rich ecosystems converge. Beneath the surface lies the Monterey Submarine Canyon, one of the continent’s largest deep-sea canyons, plunging to depths greater than two miles. Along its edges, snorkelers can explore rugged rocky reefs and towering pinnacles teeming with sea stars, anemones, and darting fish. This sanctuary offers a stunning range of underwater habitats, each shaped by the canyon’s influence and the relentless power of the Pacific.
In Hawaiian Islands Humpback Whale Sanctuary and National Sanctuary of American Samoa, volcanic lava flows have sculpted unique reef formations, with caves and swim-through arches woven through coral thickets, ideal for curious snorkelers. Across these protected sanctuaries, each dive reveals a unique underwater terrain molded by earth and ocean, inviting snorkelers into hidden worlds of natural wonder.
In Gray’s Reef National Marine Sanctuary off the coast of Georgia, snorkelers can explore sandstone ledges, rocky outcrops, and natural hardbottom ridges that rise from the sandy seafloor. These formations create a patchwork of underwater landmarks that shelter sponges, corals, and schools of fish, offering a striking contrast to the open waters of the South Atlantic.
Across these protected sanctuaries, each dive reveals a unique underwater terrain molded by earth and ocean, inviting snorkelers into hidden worlds of natural wonder.