Thousands of fish have died after a stretch of canal in Wigan became severely polluted and starved of oxygen.
Environment Agency (EA) officers had to carry out several days of urgent work on the Leeds and Liverpool Canal in Aspull after wildlife was spotted in distress due to the water conditions.
The North West Waterways raised the alarm on Boxing Day as the canal in the area near the Withington Lane bridge was discoloured and the water had a white frothy substance in it.
Dramatic videos posted on an EA Twitter feed showed fish swimming extremely close to the surface of the waterway in some difficulty and employees working to improve oxygen levels.
Pollution further up the canal from the borough is believed to be responsible for the problem and an investigation is now under way.
Environment management team leader, Graham Miller, said: “The EA responded to an incident on the Leeds-Liverpool Canal at Wigan Flight Lock over Christmas, where several thousand fish died.
“Environment officers have been on site investigating the cause of the pollution and samples have been taken for analysis.
“We are continuing to investigate the potential sources of the pollution which is suspected to be organic pollution from further up the canal network.
“Officers have been working with the Canal and River Trust and oxygen levels were improved by aerating the water.”
The Twitter feed run by the EA’s fisheries officers for the North West showed aeration initially began on December 27 and continued during the following day as oxygen levels improved overnight.
The team warned during the day on December 28 that it would take a while longer for the oxygen quantity to rise sufficiently.
The EA then identified two stretches of the canal where the low oxygen levels were particularly based and dosed these with hydrogen peroxide on December 29.
The last area to be treated was at Red Rock close to Aspull and the situation was monitored over the weekend by the Canal and River Trust.
Fisheries officers also said the situation in the canal would be reassessed this week.
The sight of the work being carried out with hydrogen peroxide pouring into the water prompted some concern among local residents, who suggested the canal had to be treated as far as Top Lock.
Environmental incidents should be reported to the EA on 0800 80 70 60.