Thames Water has been fined a record £20 million fine from the Environment Agency after pumping nearly 1.5 billion litres of untreated sewage into the River Thames.
Thames Water admitted water pollution, in incidents taking place between 2013 and 2014.
Fish and birds were amongst the various types of wildlife that died following the pollution.
Sewage spilled into nature reserves and further environmental damage was reported in the riverside towns of Henley and Marlow.
Chief executive of Thames Water, Steve Robertson, said he deeply regretted the spills but insisted things at the company had improved since it increased staff in key roles.
The fine must be paid within 21 days.
