How to Identify Sea Turtles Underwater: A Diver's Guide to the Seven Species

Ask a group of divers what they saw on a reef dive and someone will say "a turtle." Ask which kind, and the answers get vague fast. That is a shame, because sea turtles are among the easiest large marine animals to identify to species — the diagnostic features are on the shell and the face, they hold still long enough to count, and there are only seven species in the world to choose from.

Getting the identification right is not trivia. Species differ enormously in how threatened they are, what they eat, and which habitats they depend on, so a sighting logged as "turtle" is close to worthless to a researcher while a sighting logged as "juvenile hawksbill, 45 feet, on sponge-covered wall" is genuinely useful. Learning to tell them apart also changes how you dive: once you know that the animal in front of you is a critically endangered hawksbill working a sponge, you tend to stop swimming toward it.

This guide covers the three features that separate the species, a field description of all seven, what the 2025 IUCN Red List revision changed, how close you are actually allowed to get, and how to turn your photos into research data.

Three features that separate the species

Almost every sea turtle identification comes down to three things you can check in a few seconds of bottom time. Work through them in order and you will rarely be wrong.

1. Count the costal scutes

The large plates running down each side of the carapace, between the central row and the outer rim, are the costal (or lateral) scutes. Count the pairs on one side. Green and hawksbill turtles have four pairs. Loggerheads and Kemp's ridleys have five. Olive ridleys typically have six to nine, and the count is often different on the left and right sides — an asymmetry that is itself a useful clue. Leatherbacks have no scutes at all.

2. Look at the scales between the eyes

The prefrontal scales sit on the top of the head between the eyes, and they separate the two species that share a four-pair scute count. A green turtle has a single pair — two large scales, side by side. A hawksbill has two pairs. If you are photographing a turtle head-on and cannot count scutes, this alone will usually settle it.

3. Read the head and beak

Shape carries the rest of the information. A hawksbill's beak is narrow, tapered, and slightly hooked, built for reaching into crevices. A green turtle's jaw is blunt with a serrated lower edge suited to cropping seagrass. A loggerhead's head is disproportionately large, housing the jaw muscles it uses to crush conch and whelk shells. If a turtle's head looks a size too big for its body, it is a loggerhead.

The seven sea turtle species

Green turtle (Chelonia mydas)

The turtle most divers meet. Four pairs of costal scutes, one pair of prefrontal scales, a blunt head, and a smooth, non-overlapping carapace that runs from olive to brown with darker streaking. The name refers to the greenish body fat, not the shell.

Greens are the only sea turtles that become largely herbivorous as adults, grazing seagrass beds and algae, which is why they are reliable in shallow, well-lit habitat. Adults commonly reach around 3 to 4 feet of shell length. In Hawaiʻi, where they are called honu, resting greens on the reef and basking greens on the beach are both routine sights.

Hawksbill turtle (Eretmochelys imbricata)

Also four pairs of costal scutes, but the scutes overlap like roof shingles — the trait behind the species name imbricata. Two pairs of prefrontal scales, a narrow tapered beak, and a serrated rear margin on the shell. Smaller than a green, usually somewhere around 2.5 to 3 feet.

Hawksbills are the only sea turtle able to live mainly on sponges, and that diet ties them to healthy coral reef and hard-bottom habitat. It also means you tend to find them on walls and reef faces rather than over sand or grass. The IUCN assesses the species as Critically Endangered globally.

Loggerhead turtle (Caretta caretta)

Five or more pairs of costal scutes and a head you cannot miss. The carapace is reddish-brown and heart-shaped, and adults are heavy-bodied, typically around 3 feet of shell length. Loggerheads eat hard-shelled invertebrates, so look for them over rubble, rock, and offshore hard bottom rather than manicured coral.

Globally the species is Vulnerable, but the subpopulation picture varies enormously: the Northwest Atlantic and North Pacific subpopulations are assessed as Least Concern, while the Northwest and Northeast Indian Ocean and South Pacific subpopulations are Critically Endangered.

Olive ridley turtle (Lepidochelys olivacea)

One of the two smallest sea turtles, at roughly 2 feet and 100 pounds. The carapace is olive-grey, nearly round in outline, and high-domed. The giveaway is the scute count: six to nine pairs, frequently asymmetric, which no other species does.

Olive ridleys are the most abundant sea turtle worldwide and are best known for arribadas, the synchronized mass nesting events on a small number of Pacific and Indian Ocean beaches. Divers encounter them far less often than greens or hawksbills because they spend much of their lives in open water. The species is assessed as Vulnerable.

Kemp's ridley turtle (Lepidochelys kempii)

The smallest sea turtle and the most geographically restricted, with a shell length of roughly 20 to 28 inches and a nearly circular grey-olive carapace. Five pairs of costal scutes. Its range centers on the Gulf of Mexico and the western North Atlantic, and the great majority of nesting happens on a short stretch of coast in Tamaulipas, Mexico.

It is assessed as Critically Endangered, and any credible sighting is worth reporting to a regional stranding or monitoring network.

Leatherback turtle (Dermochelys coriacea)

Unmistakable and rarely seen by divers. Leatherbacks have no scutes and no hard shell — instead, a mosaic of small interlocking bones covered in rubbery skin, with seven pronounced ridges running the length of the back to a blunt point.

This is the largest turtle alive. The record individual, stranded in Wales in 1988, weighed close to 2,020 pounds. Leatherbacks dive to roughly 4,000 feet, deeper than any other turtle, and can stay down as long as 85 minutes. They feed almost entirely on jellyfish, which is why floating plastic bags are such a specific hazard to them. Globally Vulnerable, with several subpopulations — East Pacific, West Pacific, Southwest Atlantic, Southwest Indian Ocean — assessed as Critically Endangered.

Flatback turtle (Natator depressus)

The one species most divers will never see. Flatbacks are endemic to the Australian continental shelf and nest only in Australia. The carapace is low, flattened, and olive-grey with distinctly upturned edges, with four pairs of costal scutes. The IUCN lists the species as Data Deficient — not because it is doing well, but because there is not enough information to assess it.

What the 2025 Red List change means

In 2025 the IUCN reassessed the green turtle globally and moved it from Endangered to Least Concern, reflecting decades of nesting-beach protection, fisheries bycatch reduction, and harvest restrictions that have produced measurable population increases at many index sites. It is one of the clearest conservation successes in marine vertebrate management, and it is worth knowing about, because a great deal of turtle content online has not caught up.

Two caveats matter to divers, though. First, the global category masks real variation: the Central South Pacific subpopulation is still Endangered and the East Pacific and North Indian Ocean subpopulations are Vulnerable. Second, an IUCN category is a scientific assessment, not a law. All sea turtles found in United States waters remain listed under the Endangered Species Act, which makes it illegal to harass, harm, pursue, capture, or kill them, their eggs, or their hatchlings. The rules you dive under have not changed.

Where you are most likely to see them

Six of the seven species occur in United States waters — every one except the flatback. Habitat is the fastest shortcut to a species name before you have even seen the animal clearly.

• Seagrass beds and shallow algal flats: green turtles, usually feeding head-down or resting on sand between grazing bouts.
• Coral walls, reef faces, and sponge-covered hard bottom: hawksbills, typically working crevices or wedged under a ledge.
• Rubble, rock, and offshore hard bottom: loggerheads, often stationary and surprisingly tolerant of divers who hold position.
• Open blue water: olive ridleys and, very occasionally, a leatherback in transit.
• Gulf of Mexico shallows and passes: the possibility of a Kemp's ridley, which is worth reporting.

Turtles are also predictable by time of day. Greens and hawksbills often tuck under the same ledge to rest, returning to it night after night, which is why a night dive on a familiar reef will frequently show you a sleeping turtle in the same spot your guide pointed out last week.

How close is too close

The distance guidance divers encounter is inconsistent, and the inconsistency is genuine rather than a matter of one source being wrong. NOAA Fisheries' national marine life viewing guidance recommends a minimum of 50 yards from sea turtles, by land or sea. NOAA's Pacific Islands guidance for Hawaiʻi, where in-water turtle encounters are routine and unavoidable, recommends a minimum of 10 feet on land and in the water.

The practical reading: 50 yards is the national default for deliberately approaching a turtle, and roughly 10 feet is the floor when an encounter happens around you on a reef where turtles and people share the same shallow water. Neither number authorizes closing the gap. Whatever the local rule, the operating principle is the same — do not approach, do not touch, do not chase, do not ride, do not feed, and keep the interaction to a few minutes.

The mistake divers make most often

It is not touching. It is positioning. Sea turtles are air-breathing reptiles that must surface to breathe, and the single most harmful thing a group of divers can do is hover above a resting turtle to get photographs. A turtle that will not push up through a ring of divers and bubbles is a turtle that is not breathing, and a stressed animal burns oxygen faster than a calm one.

Stay beside or below, never directly overhead, and leave an obvious open corridor to the surface. The same logic applies at a ledge: a turtle backed into a crevice with divers across the opening has nowhere to go. Give it an exit and it will usually stay put and let you watch, which is the outcome everyone wanted anyway.

Gear that helps you identify and document

Identification underwater is mostly a lighting problem. Water absorbs red wavelengths within the first several meters, so a hawksbill's shell pattern at 60 feet is a grey-brown smear in ambient light and an obvious mosaic of overlapping amber scutes under a beam. A general-purpose torch from the dive lights range is enough to count scutes and check prefrontal scales. If you are also shooting photos or video, a wide-beam flood such as the SeaLife Sea Dragon 2300F COB kit lights the whole animal evenly instead of putting a hot spot on the middle of the shell — and the broader video lights range covers brighter options if you shoot wide-angle.

Use the light considerately. Keep the beam off the animal's eyes, and on night dives do not hold a light on a sleeping turtle any longer than it takes to make the identification.

For documentation, a phone in a rated housing is more than adequate. The DIVEVOLK SeaTouch 4 MAX PLUS keeps full touchscreen control underwater, which matters when you have a few seconds to frame a profile shot and no time to hunt for a physical button; the wider smartphone housings range covers other phones and depth ratings. Photo-identification does not need a professional system — it needs a sharp, well-lit, correctly angled image.

One thing to leave behind: a pointer stick has no legitimate use around a turtle, and gloves are worth reconsidering on reef dives, since divers wearing them tend to touch more. Our guide to marine life divers should never touch covers the broader case for keeping your hands off the reef.

Turning a sighting into data

Sea turtles carry individually unique facial scale patterns — the arrangement of scales on the side of the head between the eye and the jaw is effectively a fingerprint, and it does not change as the animal grows. That makes recreational divers a serious data source, because a clear side-of-head photograph can be matched against a catalog to re-identify a specific animal months or years later.

To make an image usable:

• Shoot the side of the head square-on, close enough that the scales between the eye and the jawline are sharp.
• Photograph both sides if the animal gives you the opportunity, since catalogs are often keyed to one side.
• Add a shot of the whole carapace from directly above or directly beside, which captures scute count and any distinctive damage.
• Record date, dive site, depth, and approximate shell length. A dive computer with a downloadable log makes reconstructing depth and temperature straightforward later.
• Note behavior — feeding, resting, mating, transiting — which is often the part researchers are missing.

The main global catalog open to the public is Internet of Turtles, a Wildbook platform that runs submitted facial photographs through a pattern-matching algorithm and flags likely matches for a researcher to confirm. Many regional monitoring networks feed into it and publish their own submission forms as well. If you dive the same sites regularly, submitting consistently is more valuable than a single spectacular photograph, because re-sightings are what turn images into residency and survival estimates. Our guide to becoming a citizen science diver covers how to find a program near you.

The habit that matters most

Identification and etiquette turn out to be the same skill. A diver who is trying to count costal scutes has to hold a stable position, stay off the bottom, and wait for the animal to present the angle — which is precisely the behavior that keeps the turtle calm and the reef intact. Chasing produces neither a usable photo nor a species name.

Green turtles moving to Least Concern is a reminder that this works: sustained, unglamorous protection over decades measurably brought a species back. Five of the remaining six are still in threatened categories, two of them critically endangered, and the last has never had enough data to assess. Diving in a way that lets turtles keep doing what they were doing is a small contribution, but it is the one every diver gets to make on every dive.

For more on reducing your footprint on the reef, see our guide to low-impact diving.