In 1957, the River Thames in London was declared “biologically dead” due to severe oxygen depletion caused by decades of sewage and industrial contamination. At that time, the waterway’s condition was so dire that few forms of aquatic life could survive its polluted environment.
Fast forward nearly seven decades, and the river’s revival is nothing short of extraordinary. The tidal stretch of the Thames and its estuary have transformed into thriving habitats for a variety of marine species. The latest comprehensive assessment published by the Zoological Society of London (ZSL) in January 2026 confirms that this ecological comeback is ongoing.
Marine Life Flourishes in the Thames Estuary
Among the most remarkable inhabitants are the sharks that now frequent the estuary. Scientists have identified at least five shark species in these waters, including tope and starry smoothhounds. Research suggests that the estuary serves as a crucial nursery ground, providing a safe environment for juvenile sharks to develop.
Seals have also made a significant return to the area. The Greater Thames Estuary currently supports an estimated population of approximately 2,987 grey seals and 599 harbour seals, according to ZSL’s recent data. This resurgence highlights the improving health of the river and its surrounding ecosystems.
Additionally, other marine creatures such as seahorses and eels inhabit the Thames, further indicating the waterway’s enhanced biodiversity.