American eels are catadromous, which means they live their life in freshwater but breed in the ocean. This is the other way around from anadromous fish like the striped bass and salmon that live in the ocean but return to freshwater to spawn.
A young eel is born in the Sargasso Sea, an area north of the Bahamas. The small larvae, called leptocephalus, don't swim but drift with the ocean currents for 9 to 12 months before they reach the coastal waters of North America.
Picture: American eel. Picture courtesy of U.S. Fish and Wildlife Service/Duane Raver.
The eels develop into "glass" eels before entering the brackish waters and freshwaters where they will live most of their lives. When the eels are around 1 meter (about 3 feet) long, they mature and get ready to migrate back to the Sargasso Sea where they will spawn. After spawning, the adults die and the larvae again drift north.
References and further reading
Members of the American Eel Monitoring Survey team at the Virginia Institute of Marine Science (VIMS) are counting the number of young eels that are migrating into Virginia's estuaries and freshwater lakes and pond. Their website has some great images of eels in various life stages.
Read more about the American eel and its life cycle on the website of the The Chesapeake Bay Program.