UPDATE: The judge at Aylesbury Crown Court has said that because there's a further indictment to consider, sentencing is now expected on 21 March.
Thames Water is expected to receive its largest ever fine for river pollution at Aylesbury Crown Court.
One of the country's biggest water suppliers admitted pumping tens of millions of gallons of untreated sewage into the River Thames.
The offences involved five facilities in the middle and lower Thames Valley during 2013 and 2014.
Hundreds of fish and birds died over a two-year period when "out of control" sewage treatment centres owned by Thames Water, sent untreated water into rivers in Oxfordshire and Buckinghamshire.
Other sites at Henley-on-Thames, Didcot, Oxcon., Little Marlow, Bucks., and Littlemore, Oxon., suffered failings and contributed to the River Thames, River Wye and The Thame river being polluted with human waste.
Levels of ammonia described as being "devastating to life" were detected during tests on the river at a Thames Water site at Henley-on-Thames before 50 dead fish were spotted floating on the surface of the river.
The court was told that In July 2013 an Environment Agency officer saw dead fish and spotted at least 50.
The site at Henley-on-Thames was "under-using" the capacity of its works and was dealing with 67 litres per second rather than the figure of 85 litres per second it should be able to handle. Water samples taken by Environment Agency officers in the River Thames showed oxygen levels of 93.5 per cent while downstream at Moor Ditch, levels were recorded at just 24.95 per cent.
Thames Water Utilities admitted several charges of unlawful discharge and breaching ammonia levels under the Environmental Permitting Regulations in relation to the five sites and will be sentenced on February 22 by Judge Sheridan, who has revealed he is contemplating awarding compensation to those affected.
After hearing most of the prosecution's case Judge Sheridan said: "This is likely to be the biggest fine Thames Water has ever faced."