The work included laying a new one kilometre sewer across the nature reserve, which is a site of special scientific interest and home to one of only 50 colonies of rare natterjack toads in mainland Britain, according to United Utilities.

United Utilities said it managed to push the new pipe through the inside of a larger disused sewer, avoiding the need for large-scale digging. Project Manager Roger Woodcock said finding the old abandoned pipe in such good condition was a bonus.

United Utilities added the Millom Ironworks Local Nature Reserve was likely to have weeks of disruption when the utility began an £18 million scheme to clean up the estuary.

Friends of Millom Ironworks Local Nature Reserve member and Chair of the Ironworks Management Committee Brian Crawford said “Laying the pipe this way has saved time, money and a lot of disturbance for the wildlife and people who enjoy visiting the reserve.”

Article continues below…

“When our work is done, there will be much less untreated stormwater making its way into the estuary in heavy rains, and that's great news for the seas and coast around Millom and Barrow too," Mr Crawford said.

The remainder of the sewer project is expected to take one year to complete.