A decision not to order an immediate halt to the unauthorised extraction of up to two million tonnes of sand a year from Lough Neagh is to be quashed, the Court of Appeal ruled on Wednesday.
Senior judges held that former Environment Minister Mark H Durkan took the wrong approach when he instead served enforcement notices on companies dredging without planning permission.
They directed that the Department must now reconsider whether to issue a stop notice, taking into account the precautionary principle of securing definitive evidence the activity causes no environmental harm.
Although the verdict does not mean an automatic cessation to sand extraction from the UK's largest fresh water body, Lord Justice Weatherup stressed: "The issue requires immediate attention."
And Friends of the Earth, who took legal action in a bid to bring an end to the dredging, vowed to press senior officials.
James Orr, the group's Northern Ireland Director, said: "It's up to the permanent secretary in the absence of a Minister to take the decision that the action of the Department is now unlawful.
"We will be writing today to say if you want to abide by environmental laws you need to issue a stop notice now."
Sand traders have been carrying out extraction work on Lough Neagh, a designated Special Protection Area due to its wintering population of birds, since the 1930s.
In 2015 Mr Durkan issued enforcement notices on the companies, requiring them to halt operations on the Lough.
But by lodging an appeal with the Planning Appeals Commission (PAC), the firms were able to continue their activities.
Friends of the Earth launched judicial review proceedings, claiming Mr Durkan should instead have ordered an immediate stop to all extraction.
Last year the High Court rejected claims that the Minister's decision effectively amounted to giving consent by "turning a blind eye" to the dredging.
But the group appealed the finding that there was legal authority for his decision.
They argued that it made a mockery of Northern Ireland's planning regime, and amounted to a flagrant breach of Environmental Impact Assessment and Habitats Directives.
Counsel also contended that the Minister failed to properly apply the precautionary principle of taking preventative action until proof of no environmental harm is produced.
Backing their case, Lord Justice Weatherup held that the Minister instead acted on the basis of a lack of evidence of an unacceptable impact.
"This is the wrong approach," he said.
"To approach the matter with a requirement for evidence of harm is the negation of the precautionary principle."
The judge confirmed: "The decision will be quashed.
"The Court refers the matter back to the Department so that a determination may be made as soon as possible on whether or not to issue a stop notice."