Tests have begun to determine how Whitehaven’s harbour water has turned orange.
Since late 2022, the water in Queen’s Dock changed to a rusty colour and now, engineers are working to find the cause.
Network Rail has sent experts to undertake the tests of a railway tunnel, thought to be the cause.
The tunnel, which takes trains a kilometre underground between Corkickle and Whitehaven, sometimes floods.
To cope with that excess water and keep trains running safely, it is connected to Whitehaven harbour by a culvert.
For decades water has drained from the railway into the harbour without an issue, Network Rail said, but it is believed the water, containing iron ochre, could be from historic mine workings in the area.
Network Rail is now carrying out detailed tests to find out how and where it is getting into the tunnel, and will work with the Environment Agency, Coal Authority and Whitehaven Harbour Commissioners to find a long-term solution to the problem.
The aim is to build a detailed picture to explain where the water which flows into Bransty Beck – including what makes its way into and out of the tunnel drainage system – comes from in more detail than is currently known.
Network Rail said due to the complexity of the situation, it had taken several months to appoint specialist contractors to carry out the tests.
Railway engineers have also been meeting with retired miners in the area with knowledge and expertise on where uncharted mine workings could be, as historic mining could be linked to the change in water composition, it added.
Overnight inspections of the tunnel began on Thursday after train services stopped running at 10pm.
For safety, trains are travelling at slower speeds through the tunnel due to the ongoing issue with the flood water, Network Rail added and trains can only run at 20mph instead of 40mph, meaning longer journey times for passengers and freight.
Phil James, Network Rail’s North West route director said: “We know this complex investigation work is causing frustration as it’s taking a long time, so we thank harbour users, rail passengers and local people for their continued patience.
“We’re committed to working with the Environment Agency and Coal Authority to find the source of the water impacting our railway tunnel and the harbour so we can plan next steps to find a solution together.
“Solving this is also important for our passengers and freight, whose journeys we hope will be made more reliable and faster once the source of the mysterious orange water is made clear.”
Pete Miles, Environment Agency area environment manager, said: “Analysis of water samples from Whitehaven Harbour found no evidence of sewage pollution.
“The results did show some increased metals in the water and we are working with Network Rail who are actively investigating this further to determine the potential source.”
Andy Morritt, Coal Authority head of environment strategy and sustainability, said: “We are continuing to provide assistance and expertise as required to support Network Rail’s investigations.”
Testing will be ongoing for several weeks and it is hoped the findings can inform next steps and reveal the scale of what can be done to either mitigate, reduce or in the best case scenario stop the water from entering the railway tunnel entirely.
