Oxford and Cambridge rowers have been warned off jumping into the River Thames course after high levels of E coli were found in the water.
The annual Boat Race is one of British sport's longest-running events having first been held back in 1829.
The event sees Oxford and Cambridge go head-to-head on the 4.2-mile 'Championship Course' between Putney and Mortlake.
Traditionally, the winning team will throw their cox into the water as part of their celebrations.
The winning Cox is often thrown into the water
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But a worrying discovery in the River Thames has meant that won't be possible this weekend.
River Action campaign group were conducting regular testing along with the Fulham Reach Boat Club over the span of four weeks between the end of February and end of March.
From 16 tests that were done near the Hammersmith Bridge - a part of the course rowers will race - found an average of 2,869 E coli colony forming units (CFU) per 100ml of water.
Safe levels are required to be below 1,000 CFU per 100ml, leading to new safety measures being put in place for this year's Boat Race.
River Action added that the highest level it recorded was an astonishing 9,801 CFU per 100ml.
Teams have been advised against coming into contact with the River Thames at all.
The crews will be encouraged to wash themselves at a dedicated cleansing station and to wear footwear and cover up any cuts or blisters.
River Action chief executive James Wallace said: "It is a tragic situation when elite athletes are issued with health guidance ahead of a historic race on the capital's river.
Teams have been told not to come into contact with the water
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"Our water quality results show what happens after decades of neglect by an unregulated water company, Thames Water."
The E coli bacterium is found in faeces and can cause a wide range of conditions with the worst cases leading to life-threatening problems.
The Boat Race said in a statement: “Water quality is an ongoing concern for the Boat Race.
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The Boat Race will still go ahead as planned
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“We have put in place a series of precautionary measures this year to protect the health of our athletes, which includes guidance regarding the covering up of open wounds, regular handwashing, a cleansing station at the finish area and highlighting the risks of entering the water.
“We will also be taking on board British Rowing’s recent Poor Water Quality Guidance, issued in partnership with River Action, as we look forward to the Gemini Boat Race 2024.”
