How Maine's eel elevator restored fish and attracted humpback whales

Every spring, millions of migratory fish leave the Atlantic Ocean and swim into freshwater rivers to reproduce, continuing journeys that have existed for thousands of years. On Maine's Penobscot River, however, hydroelectric dams blocked many of these ancient migrations for more than a century, causing dramatic declines in species such as American shad, river herring, Atlantic salmon and American eel. To reverse the damage, engineers introduced innovative fish passage systems, including a mechanical fish lift and a specialised eel ladder, often called an "eel elevator", allowing fish to bypass the Milford Dam safely. As fish populations recovered, something remarkable happened downstream: humpback whales began appearing near the mouth of the river to feed on the returning schools.