The Environment Agency is launching a campaign to halt the repeated pollution of a brook in Bristol.
The agency says Brislington Brook has seen a decline in water quality and wildlife because of the pollution from nearby industrial units.
Several incidents can be traced back, says the agency, to pollutants being poured into surface water drains which flow into the brook.
Officers will spend the next week educating businesses.
Brislington Brook runs through Brislington, St Annes and Broom Hill.
Victoria Freke from the Environment Agency said: "Tracing pollution caused by spillages into surface-water systems in urban areas can be very difficult.
"Unfortunately, there have been several such pollution incidents on the Brislington Brook that have had a significant negative impact on water quality and local wildlife."