Restoring Dead Rivers

Some of the most polluted rivers are making remarkable comebacks. The Thames was declared biologically dead in the 1950s. Today, over 125 fish species have returned, along with seahorses and seals.

South Korea tore down a Seoul highway to uncover the Cheonggyecheon Stream, buried under concrete for decades. The restored stream cooled the area by several degrees and created a thriving urban ecosystem.

The lesson: when pollution stops, rivers bounce back faster than any other ecosystem — insects within months, fish within years, full complexity within decades.