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An app which predicts water quality along Northern Ireland's coast is helping bathers find the safest spots to swim during unsettled weather.

The 'Swim NI' pilot project covers six beaches across counties Down, Antrim and Londonderry.

Heavy rainfall can cause pollution problems in coastal waters.

Last month was the wettest July on record in Northern Ireland, followed by a damp start to August.

At the end of July, swimmers were advised not to go into the water at Donaghadee, Crawfordsburn and two beaches in Bangor.

The warning was lifted after 24 hours.

There have also been problems with potentially toxic blue-green algae along the north coast.

On Monday, the Swim NI app predicted "poor" water-quality off Ballywalter in County Down.

The same warning was issued for the waters off Newcastle in County Down the previous day.

In the Republic of Ireland more than , including 13 in County Dublin and six in County Clare.

Beaches affected in and around Dublin include Velvet Strand, Portmarnock and Sandymount Strand.

Among the beaches being monitored by the Swim NI app are Castlerock, Portrush East Strand and Waterfoot in County Antrim, Ballyholme in Bangor in County Down, Ballywalter and Newcastle.

The app is supported by the Department of Agriculture, Environment and Rural Affairs (Daera), with involvement from the Agri-Food and Biosciences Institute.

Information from it is also available on the Keep Northern Ireland Beautiful website.

App guidance

Annika Clements, a principal scientific officer at Daera, said the app's information was based on "predictive modelling" rather than actual sampling.

"We take a sample on one day and it can take up to 24 hours to get the results, so it does mean there's always this delay in being [able] to provide advice to bathers," she said.

Ms Clements described the app as a guide.

"It's still a pilot project which means it's not perfect by any stretch of the imagination, but we are continuing to improve it and work on it, and we'd hope to roll it out to more sites in the future," she said.

On Monday, information on the Swim NI app indicated water quality at five of the six beaches featured in Northern Ireland would be "excellent".

Waters off Ballywalter were described as "poor".

Meanwhile, Daera officials will test the waters around Newcastle and Ballywalter on Tuesday.

"The reports on this app are purely predictions and not derived from water sampling," a spokesperson for Daera said.

"Please note that the predictive modelling for the sites of Newcastle and Ballywalter tends to be over-precautionary, often showing 'poor' when water samples have confirmed the water is actually safe for bathing (in terms of faecal indicator organisms)," a spokesperson for the department added.

"Daera is working with scientists at the Agri-Food and Biosciences Institute to improve the predictions for such sites. But their catchments are complex, which is a challenge for modelling."