Health Risks

In 2007 the Health Protection Agency published its Thames Recreational Users Study into the associated risks of using the Tidal River. A summary taken from the report is below.


The introduction of interventions such as the “Thames Bubbler” (a method of directly introducing oxygen to the river to increase dissolved oxygen levels), the collection of floating flotsam and jetsam from the tideway and improvements to sewage treatment works in the Thames tideway over the past 20 years has resulted in improvements to river quality as measured by the increased biodiversity of the area. Studies addressing water quality in the upper Tideway have, to date, primarily addressed the ecological and aesthetical impacts of treated and untreated effluent discharges. Few of these studies have however, addressed the potential risks to public health posed by faecal pollution of human or animal origin which have been shown to be associated with these discharges. In clear water, turbidity can be used as an indicator of pollution. In the Thames however, because of the high background levels of turbidity only very recent significant pollution events are visibly noticeable.

Floating biological matter disseminates relatively quickly after a sewage discharge, so that the plug ofsewage moves unnoticed with the ebb and flood of the tide. An earlier collaborative project between the City of London; Environment Agency and the Public Health Laboratory Service (now part of the Health Protection Agency) had shown that the microbiological quality of the Thames significantly deteriorated following rainfall events(this can be either a sustained light to moderate rainfall or a short heavy storm). This deterioration could be due to urban runoff, the operation of Combined Sewer Overflows

(CSO) overflows designed to dispose of excess rainfall runoff together with sewage, at times of pressure to the sewage system in London, particularly when high intensity rainfall events occur over the London catchment area)), or some other as yet undefined source. Thoughthere was a significant reduction of the microbiological quality of the river following CSO operation it was not known whether this was linked to an increased risk to river users. The Thames Recreational Users study commenced in May 2004 as a collaborative study between the City of London, London Port Health Authority and the Health Protection Agency with the aim of evaluating risk to users of the river and to determine whether the information gained from long term microbiological monitoring could provide useful information which could in turn be used to predict the duration of poor water quality following a rainfall event and therefore, protect public health by providing timely information on current risk to users. Microbiological quality of water is determined by using bacteria which act as an indicator of faecal pollution.

The reason we use these indicator bacteria, such as Escherichia coli; enterococci and bacteriophages (bacteriophages are small viruses that infect bacteria and can be used to indicate the presence of viruses that can cause human infection) is that these indicator microorganisms are present in much higher numbers in the faeces of warm blooded animals than the pathogens (bacteria and viruses that are capable of causing human infection) themselves and therefore much easier to detect, however, there was little evidence to link the presence of high levels of bacterial indicators of faecal pollution (pollution involving human and /or animal faecal matter and possibly commercial effluent mixed tovarying degrees) to the level of risk to human health. The previous study has also shown that pathogens with the potential to cause disease such as the Enteroviruses and bacterial pathogens Campylobacter and Salmonella were frequently present in the river; however there was no assessment or evidence that there was a significant health impact to users.


In this study we set out to determine:-

• If there is an increased risk of ill health to river users following water contact associated with rowing and canoeing compared to non-users.

• if there was an increased risk could that be measured

• If there was evidence of an increased risk of gastroenteritis with poor water quality as measured by a robust regime of water quality samples for Norovirus, enteroviruses and enteric bacteria.

• If there was an increased risk of Norovirus infection in cases compared to non cases, and the magnitude of the risk

• If trends obtained from microbiological monitoring could be used to provide timely information on water quality to the public.


The data collected to date remain the largest most accurate representation of  microbiological water quality data for the upper Thames tideway, and has shown:
• evidence that background concentrations of microbiological indicator organisms  exceed the World Health Organisation (WHO) recommended levels for recreational  use at Kew, Barnes and Putney

• that water quality improves as you move downstream from Kew to Barnes and Putney.

• using the WHO guidelines, less than 1% of days when samples were taken from the  Thames’ tideway were acceptable by the WHO guideline standard. (“no observable  adverse effect limit (NOAEL) i.e. of ≤ 40 colony forming units (cfu) /100 ml
enterococci for human health.

• ninety-one percent of sampling occasions resulted in Escherichia coli (E.coli)counts >  1000 cfu/100ml level, and would be viewed as “poor water quality” in terms of EC Bathing Water quality.(E. coli is an indicator of faecal contamination of human and /or animal origin).

• evidence of an elevated risk to the health of recreational users of the upper tideway for 2 – 4 days after CSO discharge events.

• evidence of frequent contamination with potential human pathogens including Campylobacter spp, Salmonella spp and Enteroviruses present in samples from at least one of the three sampling locations on 99% of sampling occasions, (Kew 90%, Barnes 90%, Putney 86%) and at all three locations on 65% of sampling occasions

• evidence to suggest that plugs of discharged waste-water moving with the ebb and  flood of the tide remain relatively concentrated for up to 4 days.

• samples collected up to 5 days after CSO discharge may still reflect raised levels of  indicator organisms depending on the location of the last discharged plug of wastewater.