Councils in Northern Ireland have been asked to consider putting dark dye in water-filled quarries to discourage people from swimming in them.
They were advised of the option by ex-Environment Minister Alex Attwood.
It followed a number of drowning accidents in open water during the recent hot weather, including two deaths in a disused County Down quarry.
Kevin O'Hare, 15, drowned in the quarry in Annalong on 1 June, and 39-year-old Colin Polland died trying to save him.
Following the double tragedy, Mr Attwood held a meeting with council staff, health and safety officials and members of Quarry Products Association, where the option of dyeing quarry water was discussed.
In a letter to all 26 councils, dated 9 July, Mr Attwood said it was his personal view that the prevention measure should be considered.
He wrote: "The usage of dye, in quarries, to deter trespass and use by the public for swimming, does not currently fall under any approval regime.
"The Northern Ireland Environment Agency (NIEA) however, has no objections in principle to the use of such dyes as long as they are inert and have no ecological impact on the water quality of waterways beyond the quarry in which they are initially used," his letter added.
Mr Attwood advised the councils that High Peak Borough Council in England had used pond dye "successfully" to dissuade people from swimming in a disused quarry in its area.
"When used in the correct quantities it turns the water an appealing blue colour. However, when used in excess, it turns the water brown," his letter stated.
The pond dye suggested is often used by golf clubs and is advertised as a "harmless" food-based substance that prevents underwater weed growth by blocking UV light.
A spokeswoman for High Peak Borough Council said they first tested excess use of the product last September, in a disused quarry in Buxton, Derbyshire, known locally as the 'blue lagoon'.
Chemicals left over from the quarrying process had made the water appear a bright, turquoise blue colour, and there were problems with trespassers who were using it as an outdoor pool.
This was despite the fact that the quarry chemicals had also left the water with a very high alkalinity, with a pH level similar to bleach.
The pond dye, used in excess, has since turned the water almost black, making it less appealing to swimmers.
On Tuesday, Armagh District Council told the Belfast Telegraph newspaper that it has more than 180 quarries in its district and it has offered to provide dye to the owners of five quarries.
In a statement, a council spokeswoman said its environmental health department had carried out a "desk top survey" of all the quarries in the Armagh area over the past year, and had "identified 18 potentially dangerous disused quarries".
"Since the start of June, all 18 disused quarries have been visited and a detailed inspection of each was carried out," she said.
"While none of the disused quarries met with the legal definition of 'being a public health nuisance' officers did have concerns about five of these. The owners of these five have been contacted and offered signage and dye," her statement added.
BBC Northern Ireland asked the DOE how the dye might affect swimmers who were still not discouraged by a darker shade of water.
A DOE spokeswoman said: "As the characteristics of the water in each quarry and the surrounding area differ, it is for the district councils to complete a risk assessment for each quarry and make an informed decision on each specific case.
"Regarding the effects of dye on the skin, district councils should refer to the manufacturer's website for details of each specific dye."