Thames River rebounds from 1950s dead zone to thriving wildlife habitat

In 1957, sections of London's River Thames were deemed biologically dead because of severe oxygen loss and decades of waste discharge. A January 2026 assessment by the Zoological Society of London reports that the river now hosts several shark species, numerous seals, seahorses, eels and a host of other organisms. The Greater Thames Estuary was estimated to contain about 2,987 grey seals and 599 harbour seals in 2024, with seals even being sighted as far upstream as Richmond.

The revival follows a series of measures beginning in the 1990s, including tighter wastewater regulations, the Environment Agency's oversight and the 15.5-mile Thames Tideway Tunnel, which began full operation in February 2025 and has diverted over 20 million metric tons of sewage by mid-2026. While dissolved oxygen levels have risen and pollutants like copper and zinc have fallen, the report notes ongoing challenges such as increasing nitrate pollution and a gradual rise in summer water temperatures.