How clean is the Thames?

Martin J Attrill, Professor of Marine Ecology, University of Plymouth


Many claims are made about the cleanliness Thames is, including regularly used statements such as “The cleanest metropolitan estuary in the world” or “The Thames supports over 120 species of fish”. With dolphins, seals and whales appearing in the estuary, plus a seemingly wide diversity of other mammals and birds now occurring within its environs, these statements seem well founded. However, we also see recent press reports of 1000s of fish killed by sewage in the estuary and watch the dirty brown water pass through London. So what is the story? How clean is the Thames?

To address this I’ll be taking a historical context, looking at how the modern Thames ecology and environment compares with past conditions – how clean is it now? I’ll look at how the estuary was impacted over the last 150 years, how pollution and recovery fluctuated and why during some time periods the Thames was almost dead. I’ll then look more closely at trends in water quality since the 1970s – how have things improved or deteriorated since the big clean up? Finally, I’ll assess the main current problems facing the estuary and what the future may hold.


The Thames Estuary stretches approximately 110 km (69 miles) from Teddington Weir to the North Sea beyond Southend, passing of course through central London. The development and growth of London and its population provided a major potential impact on the estuarine system, particularly in the 19th century, when London increased in size to be the largest city in the world at that time (4.7 million people), and again in the 20th century when the Greater London area evolved.

The development of London has resulted in the population utilising the Thames Estuary in several ways that have impacted the ecosystem.





This procedure also had a major impact on the water quality and health of the estuarine ecosystem. Whilst we do not have any data, it is clear the estuary was exceptionally polluted due to records of the smell produced. This reached a head in the hot weather of 1858 when the smell from the estuary was so bad that Parliament could not sit – this became known as the year of the “Great Stink”. Clearly something had to be done to alleviate the situation.

The engineer Joseph Bazelgette was commissioned to develop a plan to clean up the Thames in London. The result was an astonishing series of 161 km of gravity-powered interceptor sewers constructed in the 1860s to take all the discharges east of London to two major outfalls: Crossness on the south bank and Beckton on the north bank. This alleviated the problem in London, but created a new major pollution zone in the mid-estuary around Barking, where all of London’s waste was now discharged. Here extensive “mud” banks formed, the smell from the river prevented anyone walking along it and a major fishery, one of the largest in the country employing 1320 men, was destroyed. In 1878 a paddle steamer, the Princess Alice, collided with a cargo ship (Bywell Castle) and sank with 800 people on board. Over 600 died, with common rumours that many were overcome by the fumes from the polluted water before they could reach shore.

To solve the problem at the Barking outfalls, large settlement ponds were built to collect solid material before the water waste was discharged. The resulting sludge was dumped by boat in the outer estuary, a procedure that continued until 1998. The water quality of the estuary dramatically improved, with increased levels of dissolved oxygen that were now being measured. Fish populations, such as sprat, returned and people even bathed in the Thames off the Tower of London.


Following WWI there was a massive increase in the population of London, but conditions in the Thames remained reasonably healthy due to the overcapacity built into the sewage system by the Victorians. However, bombing of WW2 saw major damage to London’s infrastructure, and once again waste began to enter directly into the Thames. Few funds were available for sewage system reconstruction and with the large population the system could not cope. By the 1950s the estuary was probably in the worst state it had ever been. Surveys in this decade recorded oxygen levels at below 5% for 52 km and a 20 km stretch of the Thames around the two main outfalls having no measurable oxygen in the water! No fish populations were present for a 69 km stretch from Kew to Gravesend. The Thames was basically lifeless for most of its upper length, save for some hardy worms in the mud banks.

The 1960s saw economic recovery and investment in sewage infrastructure, coupled with an emerging environmental awareness. Major full treatment sewage works were constructed, small works closed and most waste diverted to the site of the two original outfalls at Beckton and Crossness. By 1976 all sewage was being fully treated and over the 1960s-1970s dramatic increases in water quality, as judged by oxygen levels, was apparent. Recovery was monitored using the returning fish community, documenting when new species returned to live in the Thames. A steady increase in species was recorded, including a lot of odd “one off” species such stingray, angler fish, seahorses and even goldfish! These are included in the total fish species (>120) ever recorded in the Thames but this is not the same as saying the Thames supports over 120 fish species! By the end of the 1970s the estuary was considered rehabilitated.


Over the last 20-30 years, the Environment Agency have been monitoring water quality in the Thames, so these data provide an opportunity to look at trends since the late 1970s. What has happened in the Thames? Has it got any better? Any worse? Stayed the same? How clean is the Thames now compared with the 1970s when it was considered recovered? I have analysed these data to look for trends in key variables that affect water quality of the estuary.




So, when we look at most measures of pollution, the Thames is probably in the cleanest state it has been in living memory, if not more. However, recent years have seen a decrease in the oxygen levels, and more dramatic minimum levels reached? Why might this be?


To understand why we are have continued problems with low oxygen events in the Thames, we have to look at three main factors that combine to influence how much oxygen is in the system and result in the one major remaining pollution issue on the Thames.



One further problem faces the Thames unconnected with storm impacts and dissolved oxygen.


Whatever we do, the estuary and its environment will be affected. A special project (Thames Estuary 2100) has been set up to come up with the best options.

To keep up with what is happening in the Thames, or join in local interest groups, visit the Thames Estuary Partnership’s Thames Web site at:

Prof. Martin J Attrill

Martin Attrill Bibliography of Thames publications


ATTRILL, M.J. ed. (1998). A rehabilitated estuarine ecosystem. The Thames Estuary: environment and ecology. Kluwer Academic Publisher, Dordrecht. 254 pp.

Research Papers

ATTRILL, M.J. & THOMAS, R.M. (1995). Heavy metal concentrations in sediment from the Thames Estuary, U.K. Mar. Pollut. Bull.30 (11): 742-744.

ATTRILL, M.J. & THOMAS, R.M. (1996). Long-term distribution patterns of mobile estuarine invertebrates (Ctenophora, Cnidaria, Crustacea: Decapoda) in relation to hydrological parameters. Mar. Ecol. Prog. Ser.,143: 25-36

ATTRILL, M.J., RUNDLE, S.D. & THOMAS, R.M. (1996). The influence of drought induced low freshwater flow on an upper-estuarine macroinvertebrate community. Water Research, 30 (2): 261-268

ATTRILL, M.J., RAMSAY, P.M., THOMAS, R.M. & TRETT, M.W. (1996). An estuarine biodiversity hot-spot. J.Mar.Biol.Assoc., UK.76: 161-175.

ATTRILL, M.J., BILTON, D., ROWDEN, A.A., RUNDLE, S.D. & THOMAS, R.M. (1999). The impact of encroachment and bankside development on the habitat complexity and supralittoral invertebrate biodiversity of the Thames Estuary foreshore. Aquat.Conserv., 9: 237-247

ATTRILL, M.J., POWER, M. & THOMAS, R.M. (1999). Modelling estuarine Crustacea population fluctuations in response to physico-chemical trends.Mar.Ecol.Prog.Ser.178: 89-99

POWER, M, ATTRILL, M.J. & THOMAS, R.M. (1999). Heavy metal concentration trends in the Thames Estuary. Water Res.33: 1672-1680.

POWER, M., ATTRILL, M.J. & THOMAS, R.M. (1999). Trends in agricultural pesticide (Atrazine, Simazine, Lindane) concentrations in the Thames Estuary. Environ.Pollut. 104: 31-39.

ATTRILL, M.J., & POWER, M. (2000). Modelling the effect of drought on estuarine water quality. Water Res.34: 1584-1594.

ATTRILL, M.J., & POWER, M. (2000). Effect on invertebrate populations of drought induced changes in estuarine water quality. Mar. Ecol. Prog. Ser.203: 133-143.

POWER, M., ATTRILL, M.J. & THOMAS, R.M (2000). Temporal abundance patterns and growth of juvenile Clupeidae (herring and sprat) from the Thames estuary 1977-1992. J. Fish Biol., 56: 1408-1426.

POWER, M., ATTRILL, M.J. & THOMAS, R.M. (2000). Environmental factors and interactions affecting the temporal abundance of juvenile flatfish in the Thames Estuary. J. Sea Res. 43 (2): 135-149.

POWER, M. & ATTRILL, M.J. (2002). Factors affecting long-term trends in the estuarine abundance of pogge (Agonus cataphractus). Estuar. Coast. Shelf Sci, 54: 941-949

ATTRILL, M.J. (2002). A testable linear model for diversity trends in estuaries. J. Anim. Ecol., 71: 262-269.

POWER, M., ATTRILL, M.J. & THOMAS, R.M. (2002). Environmental influences on the long-term fluctuations in the abundance of gadoid species during estuarine residency. J. Sea Res., 47: 185-194.

ATTRILL, M.J. & POWER, M. (2002). Climatic influence on a marine fish assemblage. Nature417: 275-278.

ATTRILL, M.J. & RUNDLE, S.D. (2002). Ecotone or ecocline: ecological boundaries in estuaries. Estuar. Coast. Shelf Sci, 55: 929-936

POWER, M. & ATTRILL, M.J. (2003). Long-term trends in the estuarine abundance of Nilsson’s Pipefish (Syngnathus rostellatus). Estuar CoastShelf Sci 57: 325-333

ATTRILL, M.J. & POWER, M. (2004). Partitioning of temperature resources amongst an estuarine fish assemblage. Estuar. Coast. Shelf Sci. 61: 725-738.


© Professor Martin Attrill  Gresham College, 16 October 2006