Newry, Mourne and Down District Council closed Camlough Lake in south Armagh and Castlewellan Lake in Co Down to the public for two months in July and August 2025 due to public health concerns.

Water tests conducted by the Northern Ireland Public Health Laboratory at Belfast City Hospital detected E. coli and Intestinal Enterococci in samples from both lakes during the closure period.

A council spokesperson stated the authority could not definitively identify the pollutant or its source.

The Department of Agriculture, Environment and Rural Affairs reviewed the July and August 2025 sampling data. Its spokesperson noted the lakes regularly met minimum inland bathing water standards for those bacteria in the limited data provided.

Bacterial contamination can originate from sewage inputs, agricultural runoff, wildlife, stormwater, failing septic tanks, or natural sediment disturbances, according to the DAERA spokesperson.

The lakes are not designated bathing waters. DAERA advises against swimming 48 hours after heavy rain and to avoid water if blue-green algae is suspected.

The council plans major recreational investments at both sites, including a water activity facility at Camlough Lake funded by £2.8 million in UK Levelling Up funds.

The council's economy, regeneration and tourism committee agreed to engage with DAERA on improving open waterway quality.