TARMAC Heavy Building Materials has been fined nearly £7,000 for polluting a river in the West Midlands.
The prosecution was brought by the Environment Agency under the Water Resources Act.
Tarmac pleaded guilty at Biggleswade Magistrates' court to polluting the local Broom Brook in Bedfordshire with runoff of surface and process water from the gravel processing area at Broom Quarry.
The court heard that the stretch of water had been turned orange.
An Environment Agency officer traced the pollution back to a discharge of silty water from the quarry.
Area environment protection manager Paul Wright said: 'This pollution occurred through poor site management and could have been avoided.
'Companies must accept responsibility for the systems they operate and carry out regular checks to ensure no harm comes to the environment.'