Evidence of sewage polluting the Kent coastline was locked in cupboards to stop an investigation, a court has heard.
Employees at Southern Water took documents from Environment Agency investigators and tried to bar them from entering waste treatment works in an attempt to block the investigation into pollution of protected beauty spots on England’s south coast.
The water company has pleaded guilty to 51 counts of dumping waste, including raw sewage, into the sea between 2010 and 2015. The sewage dumping took place in areas including Whitstable, Herne Bay and the Solent, much of which has protected environmental status.
On Wednesday, a judge at Canterbury Crown Court heard that employees of the firm tried to stop officers from the water regulator inspecting sites in Chichester, Queenborough and Portswood in July 2016.
Andrew Marshall, acting for the Environment Agency, told the court that on one occasion records were taken from regulator staff and locked in a van, and on another documents were locked in a cupboard.
"Across various sites, co-ordinated by senior officers including a senior lawyer, the defendant company placed itself in opposition to the agency," Mr Marshall said.
The investigation was frustrated "in an unprecedented way for what might be considered an ordinary lawful company, rather than someone operating on the margins," he added.
Five employees were convicted of obstruction of justice as a result of their actions, though two later had their convictions quashed.
Later, the court heard that the discharges were likely to have been the reason for contaminated shellfish being discovered in the area, which risked causing norovirus in people who ate them – something that, in rare severe cases, could be fatal.
The hearing continues, with sentencing expected to take place later this week.
Earlier in the week, the court heard that the investigation was the "worst case brought by the Environment Agency in its history" and caused by "a deliberate lack of control and investment".
The investigation, known as "Operation Garden", was launched following high levels of faecal bacterial contamination found in the coastal waters.
Tanks were kept full and allowed to turn septic rather than being treated as required by law, with undiluted sewage released directly over shellfish beds, the court was told.
On Wednesday Mr Marshall said customers of Southern Water had paid escalating bills on the understanding that their money would be used in part to improve and maintain the company’s equipment. This meant people had been "paying for sewerage services that were in part not provided," he said.
The company has made profits of more than £200 million in each of the past three years, the court heard.