Health chiefs are to investigate if pollution in the Thames is affecting people who regularly use the river.
The Thames flows through the heart of London
Millions of tonnes of raw sewage have been pumped into the Thames in recent weeks after heavy rain.
Hundreds of thousands of fish have been killed and there are fears that it may affect the health of the many rowers, kayakers and sailors who use the river.
The year-long study will be carried out by the Health Protection Agency and the London Port Health Authority.
The capital relies on antiquated Victorian sewers to treat water flushed from homes and rainfall from drains.
However, the network of underground tunnels is unable to cope if there is heavy rainfall, causing untreated sewage to be pumped into the Thames.
It is a long-standing problem. However, August has proved to be particularly bad.
Hundreds of thousands of tonnes of raw sewage have been pumped into the river on at least three occasions in recent weeks.
This has caused oxygen levels to plummet, killing thousands of fish.
There has also been anecdotal evidence it has caused problems for recreational users of the river.
Officials at Richmond canoe club say many of its members have fallen ill in recent weeks.
The study is one of the first to look at the health effects of regularly using a tidal river like the Thames.
Previous studies have tended to look at the risks of being exposed to polluted sea water.
They have found that exposure to contaminated water can lead to gastrointestinal illnesses.
Researchers hope this latest study will provide them with a clearer picture of the risks to health of using the Thames regularly.
The study is expected to get underway in the autumn and the results will be published in a peer-reviewed journal.
The Environment Agency says that the untreated sewage will remain in the Thames for another few weeks.
"There is still sewage in the Thames and it will take a few more weeks to clear," a spokesman told BBC News Online. "It moves slowly down the river."
Meanwhile, the HPA advises recreational users of the Thames to steer clear of the river after heavy rainfall.
"People should not use the Thames tideway for recreational purposes following heavy rainfall in the London region and to allow sufficient time for the river to clear," a spokeswoman said.