Jersey Water has dyed the water a florescent shade of green to locate a 1960s sub-sea tunnel.
Working with Ports of Jersey and the Government’s Infrastructure and Environment Department, the utility company used tracing dye to find the tunnel's entrance.
It is used to move seawater from the shoreline to the desalination plant but before yesterday (20 April) the location was unknown.
The tunnel was handmade by miners in 1969 who intentionally collapsed the entrance on completion.
Jersey Water needed to find the tunnel entrance to assess its condition as part of the company's plan to upgrade the desalination plant.
Head of Production Operations, Mark Manton, says the exercise was successful in locating the precise entrance to the submerged seawater tunnel:
"We used a safe, biodegradable green dye to highlight the tunnel entrance.
It is not in any way harmful to the environment or marine habitat and soon dissipates."
Using the bright green dye is common practice for utility companies when conducting exploratory environmental studies so islanders should not be worried.