Thames River Revival (1957-Present)
London's River Thames was declared "biologically dead" in 1957, with no measurable dissolved oxygen in central London stretches. The last Thames salmon had been caught in 1833. Industrial waste and 3 million residents' untreated sewage had made the river uninhabitable for aquatic life.
Treatment of all sewage entering the Thames began in 1976. "Thames Bubbler" oxygenation barges deployed starting in 1988. A salmon appeared in 1974, prompting a restocking program.
The Thames is now considered one of the world's cleanest urban rivers. Over 125 fish species and 400 invertebrate species have returned. Salmon are occasionally spotted, though populations remain inconsistent.
Like Boston Harbor, the Thames required decades of sustained investment to transform from notorious cesspool to environmental success story—proving that even "biologically dead" waters can recover.