In England’s Thames River, a little more than a century ago, runs of young eels, each about two inches in length, formed a densely-packed column five inches wide that ran uninterrupted for miles. Indeed, the word for a young freshwater eel, elver, is thought to have come from a phenomenon in mid-May on the Thames that eel fishermen used to term the “eel fair.”

These days, however, an eel caught in the St. Lawrence, the Thames, or the rivers of America’s Upper Midwest is an aberration. The range of American and European eels is shrinking dramatically and their total populations have fallen sharply. Populations of freshwater eels the world over — from South Africa, to Indonesia, to Australia — are in decline as the mysterious creatures have fallen victim to hydropower dams that macerate them on their downstream migrations, to coastal and river development that destroys or degrades their habitat, and to fisheries working to satisfy a robust demand for eels in Asia, especially in Japan.

Read the complete story from Yale Environment 360.