Are there freshwater eels? Yes, and they’re some of the most remarkable fish on the planet. The true freshwater eels spend most of their lives in rivers, lakes and ponds on every continent bordering the Atlantic, Indian and western Pacific Oceans, yet every one of them was born in the sea and will return there to spawn. On top of those, a handful of unrelated fish that live in fresh water carry the eel name. This guide sorts out the types, explains where each lives, and answers a question I get as a Florida-focused writer: which eels actually live in Florida’s fresh water?

The true freshwater eels: genus Anguilla

One genus, a worldwide distribution and the same strange life cycle.

All true freshwater eels belong to a single family, Anguillidae, and a single genus, Anguilla. Depending on how subspecies are counted, there are about 16 to 19 of them. They share a life history called catadromy: they hatch in the ocean, drift as transparent leptocephalus larvae to the coast, enter rivers as glass eels, grow for years as yellow eels in fresh or brackish water, then return to sea as silver eels to spawn once and die. Our eel life cycle guide covers each step.

Freshwater eels are found along coasts and rivers of the North Atlantic, the Indian Ocean and the western Pacific, from Europe and eastern North America to East Africa, Asia, Australia, New Zealand and the Pacific islands. Strikingly, there are none on the Pacific coast of the Americas or along most of the South Atlantic, probably because ocean currents there don’t carry larvae from suitable spawning areas.

Major types of freshwater eels

The best-known species, region by region.

Some freshwater eels are told apart by the length of the dorsal fin. In “longfin” eels the dorsal fin starts well forward, close to the pectoral fins, while in “shortfin” eels it starts further back, closer to the vent. Colour, mottling and range also help.

Giant freshwater eels

The biggest river eels live in the Indo-Pacific.

The heavyweights of fresh water are the giant mottled eel and the New Zealand longfin eel, both of which can approach 2 m and exceed 20 kg. The Australian longfin eel is not far behind. These giants are almost always females, which keep growing for many years before migrating to spawn. In some places, such as streams on the island of Huahine in French Polynesia, big eels are sacred and fed by villagers, which is why they can grow so large and become local celebrities. Pacific legends like Sina and the eel grew from people living alongside these animals. For record sizes, see the largest eel ever caught.

Freshwater eels in Florida

One native true eel, one invader and a few look-alikes.

The only true freshwater eel native to Florida is the American eel. It lives throughout the state in rivers, creeks, lakes, spring runs, canals and brackish estuaries, from the Panhandle to the Everglades. Florida’s glass eels arrive from the Sargasso Sea and move up rivers such as the St. Johns, and adults hide by day under ledges, logs and vegetation. Divers and snorkelers in clear springs sometimes spot one tucked into the limestone.

Florida also has an unwanted “freshwater eel”: the Asian swamp eel or rice field eel, an air-breathing fish from Asia established in canals around Tampa and Miami-Dade, including near Everglades National Park. It lacks pectoral fins and has a single gill slit under the throat, unlike the American eel. Florida’s freshwater systems also hold native and introduced fish that people sometimes call eels, including the native lampreys of a few northern Florida streams and aquarium spiny eels occasionally released by owners. In brackish water and along the coast you may also see snake eels and morays, which are marine.

Here in Florida, the rule for anyone who catches an eel-like fish is simple: if it has pectoral fins and gill openings on its sides, it’s probably an American eel and can be released; if it has no pectoral fins and a slit under its throat, it may be a swamp eel and should be reported to the state wildlife agency rather than released.

Freshwater “eels” that aren’t true eels

Several groups borrowed the name.

Swamp eels (family Synbranchidae), including the rice field eel, are air-breathing fish of tropical fresh waters in Asia, Africa and the Americas. Spiny eels (family Mastacembelidae) of Africa and Asia have long snouts and rows of small spines along the back; the fire eel is a popular aquarium example. The electric eel is a South American knifefish. Lampreys are jawless fish. None of these are related to Anguilla, though all have the long, flexible body that makes “eel” such a tempting name.

There are also a few morays that enter fresh water. Some species in Southeast Asia and the Pacific live in river mouths and the lower reaches of rivers, and a few are sold in the aquarium trade as “freshwater morays”, though they usually do best in brackish water.

Where freshwater eels live and what they need

Almost any connected water body.

Freshwater eels are found in an extraordinary range of habitats: large rivers, mountain streams, lakes, ponds, marshes, estuaries, coastal lagoons and even wells and farm ponds. They prefer places with cover, such as rocks, roots, undercut banks or soft mud they can burrow into. Their main requirement is a connection to the sea, because every eel must arrive from the ocean as a glass eel and eventually return to spawn. That’s why dams and weirs are such a problem for eels. Eel ladders, fish passes and safe downstream routes for migrating silver eels are among the most important conservation measures. Freshwater eels eat insect larvae, worms, crayfish, snails and fish, as described in what eels eat.

Why freshwater eels are in decline

An animal that needs both ocean and river is vulnerable twice over.

The European eel is listed as Critically Endangered, and the American and Japanese eels as Endangered. The reasons overlap: heavy fishing of glass eels to stock Asian eel farms, dams that block migration, hydropower turbines and pumping stations that kill silver eels, habitat loss, pollution, an introduced swim-bladder parasite and changing ocean conditions that may affect larval survival. Illegal trade in glass eels has become a major wildlife crime. My view, after years of writing about ocean conservation, is that eels are one of the clearest examples of why rivers and oceans have to be managed together. Protect an eel’s river and lose its ocean, or the other way round, and you lose the eel.

How to identify a freshwater eel

A few features separate true eels from the look-alikes.

If you’ve caught or spotted an eel-shaped fish in fresh water, start with the fins. True freshwater eels have a pair of small pectoral fins just behind the head and a long fin that runs along the back, around the tail and along the belly. Next, look at the gills: a true eel has a small gill opening on each side of the head, just in front of the pectoral fin. Then look at the mouth. Freshwater eels have proper hinged jaws, with the lower jaw slightly longer than the upper.

A swamp eel has no pectoral fins and a single gill slit under the throat. A spiny eel has a long, pointed, fleshy snout and a row of small, separate spines along its back in front of the soft dorsal fin. A lamprey has no jaws at all, just a round sucker, and a row of seven small gill pores along each side. An electric eel has no fin along its back, only a long fin along its belly, and it must come up to breathe air. Once you know these features, it takes only a few seconds to tell them apart.

Keeping freshwater eels

Possible, but not for most home aquariums.

True freshwater eels are rarely kept by hobbyists, partly because they grow large and live a very long time, and partly because many species are protected. They’re also expert escape artists that can squeeze through small gaps and survive for some time out of water. Spiny eels such as the fire eel are more common in the aquarium trade but also grow big. Anyone thinking about an eel should research its adult size, lifespan and legal status first, and never release one into the wild.