Northern Ireland Water cannot say how much diluted sewage is being released into Strangford Lough and other waterways across Ards and North Down, because most storm overflows in the borough lack monitoring equipment.

Figures from the Department for Infrastructure show that of 231 storm overflows, 94 had event duration monitors installed in 2025. Those monitors recorded 2,159 spill events. No monitors are in place on the remaining 137 overflows, leaving no record of how often they discharge or what volume they release. Even where monitors exist, they log only start, end and duration; volume is estimated by computer simulation.

This follows earlier confirmation that a single Newtownards pumping station releases tens of millions of litres of diluted sewage into the lough each year.

Storm overflows act as pressure relief valves in the sewerage network. During heavy rain they release excess wastewater into designated watercourses to prevent flooding of homes and businesses. The Northern Ireland Environment Agency assesses each overflow against criteria including whether spilled wastewater exceeds normal concentrations of foul water. In sensitive waters such as bathing and shellfish areas, an overflow is acceptable only if it spills no more than three times during the bathing season, or ten times per year for shellfish waters. Ards and North Down currently has 119 overflows classified as unsatisfactory, 44 satisfactory, 62 to be determined and six not modelled.

James Kilpatrick from Killyleagh, a critic of Northern Ireland Water, said the monitoring data show a serious gap. He said the devices provide a real record of when an overflow operates, how often and for how long, but not the volume discharged. At unmonitored sites there is no basic record at all. As extreme rainfall events become more frequent, he said, more information is needed about what happens on the ground.

He argued that monitoring alone cannot fix the problem and that the only long-term answer is investment in wastewater infrastructure. The Department for Infrastructure should make that a capital investment priority, he said. He described an ageing sewerage system that cannot cope with modern demand and more extreme weather, and said the unquantified discharges affect marine species, coastal environments and human health. He called for upgrades that reduce the need for storm overflows.