NI Water has said "a number of items of work" have to be carried out to ensure the future safety of Northern Ireland's two largest reservoirs.
The organisation made the comments after it emerged that planning applications for developments close to Silent Valley and Ben Crom reservoirs are being held up until the work is completed.
NI Water did not detail precisely what work needs to be carried out at the reservoirs.
Issues were identified in routine inspections in 2018, however NI Water has insisted the problems are not a risk to the structural integrity of the reservoirs.
It is understood, however, that planning applications for developments downstream are not currently being approved.
The Rivers Agency, which manages flood risks in Northern Ireland, recently informed Newry, Mourne and Down District Council planners it had not been updated on the condition of Silent Valley and Ben Crom following their inspection.
This means the reservoirs do not meet the planning conditions required for development next to them.
Silent Valley and Ben Crom provide water for most of Co Down and a large part of Belfast and capable of supplying 30 million gallons of water each day. They hold a combined five billion gallons of water.
Speaking to the Belfast Telegraph, DUP councillor for the Mournes area, Glyn Hanna, said there is a backlog of applications that could take "months if not years" to clear.
"There is at least six or seven major planning applications in the area that have been affected by this situation, including a massive, £20m housing development," he said.
"There are also at least 30 to 40 individual applications that I know of that are in limbo right now because of this.
"NI Water need to tell us what exactly going on. Right now all we've heard is that the problems will be fixed in the short-to-medium term. How long is 'medium term'? That could be two or three years. We need to know exactly what works are they proposing, when they're going to be carried out and how much it's going to cost.
"Let's also not forgot that, especially with the larger developments waiting to go ahead, jobs depend on these. This needs to be sorted, for everyone's peace of mind."
Mr Hanna also referenced an incident earlier this year in the town of Whaley Bridge in Derbyshire, where 1,500 residents had to be evacuated after the dam wall of a reservoir was damaged by rain.
"You have to bear in mind these are two of the largest dams in Northern Ireland and with the pressure of water going into those dams, it takes very little to go wrong with them to cause a hazard," he said.
An NI Water spokesperson said safety has always been their "number one priority" and they manage and maintain their reservoirs according to the Reservoir Act 1975, which includes weekly, monthly and yearly inspections, as well as reports every decade.
“The latest Section 10 inspections carried out in April 2018 highlighted a number of items of work to be undertaken to ensure the reservoirs continue to remain safe into the future," the spokesperson said.
"This is to be expected and is not a reflection of poor maintenance practices but is rather to mitigate against deterioration into the future.
“NI Water will proceed with the identified work, ensuring it is completed as per the recommendations of the Independent Reservoir Panel Engineer. This will ensure the maintenance of the Reservoirs continues in line with good industry practice."
The spokesperson added that the issues regarding planning applications have emerged due to how monitoring reservoir management has changed, rather than any actual change in NI Water’s inspections and maintenance.
"DfI Rivers and DfI Water Policy are working to try to find a resolution to this issue with planning applications," they added.
NI Water did not state, however, when the work on Silent Valley and Ben Crom will be carried out.