Northamptonshire Police are investigating how thousands of litres of fuel leaked into the Grand Union Canal at Gayton Marina.
Firefighters were called shortly before 4.15am on Saturday to discover a highly inflammable fuel from a pipeline near the marina was leaking directly into the water.
Assisted by the Environment Agency, the Canal and River Trust and specialist contractors, an operation was started immediately to try stop the leak and to remove the fuel from the surface of the water.
The area affected has been contained to about a 600-metre stretch from the Blisworth Arm, running south towards the M1 at Rothershorpe.
The vapour created can cause breathing difficulties and as a result 10 people were evacuated from the immediate area and were individually assessed by triage staff from the East Midlands Ambulance Service. They were then placed in temporary accommodation by staff from Northamptonshire County Council s Emergency Planning Service.
Police have also searched all 150 boats in the immediate area to check if anyone else was on board.
Chief Supt Paul Fell, who is leading the operation for Northamptonshire Police, told Connect FM: ” I d like to reassure people this leak will have no detrimental effect on fuel supplies in the local area. However, this was a criminal act which has had very significant environmental consequences in that stretch of the canal.
“We are appealing for any witnesses who may have seen anything suspicious in that area to contact us as soon as possible on 101 or Crimestoppers anonymously on 0800 111 222.”