The American eel uses ocean currents to move from its natal waters, perhaps using cues from the currents or salinity to time its metamorphoses. Having survived at least one ice age, American eel seems to be a flexible species well-equipped to withstand the short- and long-term cycles and fluctuations inherent in ocean dynamics.
American eels swim up freshwater streams to mature, others remain and mature in both estuarine and marine waters, and still others move between habitats. Like many other species, American eels no longer have access to much of their historical habitat because of dams and other obstructions in rivers. These eels, particularly silver females migrating downstream, also die in the turbines of hydropower plants. Contaminants, too, may impair eels, may most likely affect the eels during their long ocean migration.