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Swim NI

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Navigating the bathing season

Swim NI is your number-one safety guide to a successful day at the beach, predicting updates on existing water quality at some of Northern Ireland’s best coastal spots during the bathing season.

Powered by computer-modelling technology, it predicts the cleanliness of our waterways so that you don't have to.

Access water-quality predictions by visiting this page or by downloading the Swim NI app.

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Daily water quality predictions

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Safeguarding your swim 

Clean waters are central to our physical and mental wellbeing, giving us an important food source and vast open spaces for recreational activities. However, when levels of water pollution increase due to events such as flooding, animal fouling or low annual sunlight, it poses potential risks to our health.

Swim NI is an early warning system that protects bathers against exposure to two types of bacteria – intestinal enterococci and escherichia coli (E. coli) – that may lead to unpleasant illnesses like gastroenteritis and ear infection. 

Important: Swim NI does not warn against blue-green algae blooms. Please follow the local guidance in place for Harmful Algal Blooms (HAB).

The pilot project operates from 01 June to 15 September (the bathing season) each year and reports on six beaches throughout Northern Ireland: Ballyholme, Ballywalter, Castlerock, Newcastle, Portrush (Curran) and Waterfoot.

How it works

The prediction model analyses up-to-date rainfall levels and historical site samples to classify water levels as either excellent or poor. These predictions are then communicated each day during the bathing season through the Keep Northern Ireland Beautiful website and the Swim NI app.

EU Swim Project History


From 2014-2020, Swim NI was formerly known as EU Swim – a cross-border research programme aimed at developing a live bathing water quality prediction system for six beaches in Northern Ireland and three in the Republic of Ireland (Enniscrone, Lady’s Bay, and Clogherhead).

The project was funded by the EU’s INTERREG VA programme, managed by the Special EU Programmes Body (SEUPB), and match-funded by the Department of Agriculture, Environment and Rural Affairs in Northern Ireland (DAERA), and the Department of Housing, Planning and Local Government in Ireland. Total investment amounted to €1,048,966.90.

The previous lead partner in the project was University College Dublin (UCD), supported by Agri-Food and Biosciences Institute (AFBI) and Keep Northern Ireland Beautiful. Upon its completion in December 2020, UCD transferred all six NI-based bathing water quality prediction models to AFBI, who continued to refine the models by gathering environmental water samples over the 2021 bathing season. Since September 2019, DAERA has approved funding for a new EU Swim legacy project, Water Quality Prediction Models Impact DAERA Schemes (WQPMIDS), that would retain AFBI as research partner and Keep Northern Ireland Beautiful as communications partner. 

On 01 June 2022, Swim NI launched to coincide with the beginning of the bathing season. The original predictive aim of the project remains intact and all Northern Ireland beach locations are unchanged.

Swim NI FAQs

Dip into some of the key questions about Swim NI’s water quality predictions and app.  

What is Swim NI?

Swim NI is a water quality prediction guide that helps swimmers in Northern Ireland stay safe when bathing at six of our most popular beaches.

With daily updates on predicted water quality, the Swim NI app acts as an early warning system to protect bathers against potential exposure to bacteria that can cause sickness and infections.

What dangers does Swim NI warn against?

Swim NI water quality predictions protect bathers from exposure to potentially harmful bacteria. 

High levels of these bacteria in the water can lead to gastroenteritis, ear infections and other unpleasant illnesses.

Where can I get Swim NI water quality predictions?

The easiest way to get Swim NI water quality predictions is to download the Swim NI app from Google Play or the App Store

This will give you access to daily updates on the predicted water quality at six beaches in Northern Ireland during the bathing season.

The Swim NI app also includes useful information about the six beaches, including an overview of each beach’s facilities, awards and lifeguard patrol times.

How does Swim NI work?

Swim NI uses models that combines historical water sample results and hydrological and meteorological data from the catchments of six beaches across Northern Ireland with weather forecasts for each of those sites.

These models then predict the bathing water quality classification at each site for every day of the bathing season.

How does the Swim NI predictions model work? 

Swim NI's prediction model uses data from multiple locations within the catchment areas of each of the six beaches we monitor. This provides historical rainfall data from across each catchment area. 

The rainfall data is calibrated using historical water quality samples, which helps us to create a model that shows the correlation between rainfall across the catchment area and coastal water quality. 

All that data is then combined with water quality compliance samples and up-to-date rainfall data from weather stations, river stations and gauges across the catchment area to predict what the water quality will be each day. 

Why is Swim NI needed?

The amount of rainfall we get in Northern Ireland can significantly impact coastal water quality. Heavy rain causes contamination from sewer overflows and run-off from farms to be washed into the sea. 

Flooding, animal fouling or low levels of sunlight all increase the likelihood of contamination that can cause illness and infection when people are exposed to it. 

Swim NI predicts the likelihood of coastal waters being contaminated by short-term pollution so that bathers can make informed decisions before entering the water.

Where do you do water quality testing?

Swim NI’s water quality predictions use computer modelling technology and analysis based on historical water samples and the latest rainfall levels at the beaches we cover. We continue to improve the models using data from new water samples, but the predictions are not based on water samples taken that day.

The Department of Agriculture, Environment and Rural Affairs (DAERA) is responsible for bathing water quality in Northern Ireland. DAERA carries out water quality testing to make sure that coastal waters around Northern Ireland are of a high enough quality for bathing.

To do this, it monitors and classifies water quality at 33 sites across Northern Ireland between May and September. See the latest bathing water quality results and compliance levels via NI Direct.

Which beaches does Swim NI cover?

The six beaches currently covered by Swim NI’s water quality prediction models are Ballyholme, Ballywalter, Castlerock, Newcastle, Portrush (Curran) and Waterfoot.

We can’t predict water quality at other sites because we have yet to develop models for further sites.

How were Swim NI sites chosen?

At the start of what was then the EU Swim project, six beaches in Northern Ireland were selected for the pilot project.

All six beaches — Ballyholme, Ballywalter, Castlerock, Newcastle, Portrush (Curran) and Waterfoot — were included because a potential public health risk had been identified.

Beaches such as Ballyholme, Newcastle and Portrush were chosen due to their high footfall. The sites at Castlerock and Portrush were also chosen because they have cross-border tidal waters. 

Why can’t I see a water quality prediction for the beach where I plan to bathe?

Swim NI is a pilot project covering six beaches in Northern Ireland. For water quality advice on more beaches in Northern Ireland, please visit NI Direct for water quality results on the 33 bathing sites monitored by the Department of Agriculture, Environment and Rural Affairs (DAERA). 

Is it safe to bathe if Swim NI’s daily water quality prediction classifies a beach as Excellent?

There are always some risks associated with bathing in the sea. Swim NI’s water quality predictions help you to minimise those risks.

A prediction of Excellent water quality doesn’t guarantee that it’s safe to bathe. Our prediction model doesn’t include blue-green algae blooms, local weather conditions and other factors that could impact the safety of your swim. 

Check NI Direct water quality results and notices at the beach or on social media before entering the water. 

Will Swim NI add more beaches to the app?

Swim NI is currently a pilot project focused on six beaches around Northern Ireland’s coast. While we do hope to expand our water quality predictions to cover more sites in the future, there are no immediate plans to do so.

Since our prediction modelling is based on detailed studies of how weather affects water quality at each site, adding more beaches to Swim NI is not as straightforward as conducting water testing at new sites. 

When does Swim NI make water quality predictions?

Swim NI operates during the bathing season, giving daily water quality predictions between 1st June and 15th September each year.

Daily water quality predictions are available at 9am every morning during the bathing season.

Can I use Swim NI outside of the bathing season?

No, Swim NI’s water quality prediction model is based on historical data from previous bathing seasons. Outside of the bathing season, the prediction model does not work and we do not share daily water quality predictions.

Why is the Swim NI water classification different to other publicly available water quality advice for the same beach?

Swim NI water classifications are predictions based on historical data and up-to-date rainfall forecasts. They are designed to inform swimmers of the likely water quality on any given day during the bathing season.

Other water quality advice may differ depending on how the data is collected. For example, Department of Agriculture, Environment and Rural Affairs (DAERA) water quality classifications are based on weekly water quality monitoring. Water samples taken at the site may show issues in water quality that would not be indicated by our prediction modelling.

On the other hand, Swim NI predictions will highlight water quality issues that other water quality advice does not show. For example, heavy rainfall after a weekly sample has been taken might reduce water quality to a lower level than the stated classification for that week, whereas Swim NI’s daily water quality prediction will factor in the impact of the rainfall.

Does Swim NI warn against blue-green algae blooms?

No, Swim NI’s prediction modelling is based on historical water quality testing results for faecal indicator bacteria, not blue-green algae. That means that the presence of potentially toxic blue-green algae, are not factored into our water quality predictions.

For up-to-date information on blue-green algae in Northern Ireland, please follow the latest guidance on the Department of Agriculture, Environment and Rural Affairs (DAERA) website and any notices at beaches where you plan to bathe. 

What is the history of the Swim NI project?

Swim NI started life as EU Swim, a cross-border research programme that ran between 2014 and 2020. 

Using funding from the EU’s INTERREG VA programme and match-funding from the Department of Agriculture, Environment and Rural Affairs (DAERA) in Northern Ireland and the Department of Housing, Planning and Local Government in Ireland, EU Swim invested more than €1 million in developing a bathing water quality prediction system for six beaches in Northern Ireland and three in the Republic of Ireland.

Upon completion of the project in 2020, EU Swim’s lead partner, University College Dublin, transferred the bathing water quality prediction models for the six beaches in Northern Ireland — Ballyholme, Ballywalter, Castlerock, Newcastle, Portrush (Curran) and Waterfoot — to the Agri-Food and Biosciences Institute (AFBI), which had also been involved in the EU Swim project.

DAERA approved funding for an EU Swim legacy project with AFBI responsible for research and Keep Northern Ireland Beautiful overseeing communications. The legacy project ultimately became Swim NI, which launched on 1st June 2022. AFBI has continued to refine the prediction models and gather additional water samples to improve the accuracy of Swim NI predictions.

What are the health risks of bathing when water quality is poor?

Swimming in poor-quality bathing water increases the risk of infection caused by bacteria and viruses from faecal matter. This includes a higher risk of contracting eye, ear, skin and throat infections, gastroenteritis, E. coli and hepatitis.

What is the overall water quality like in Northern Ireland’s coastal waters?

Northern Ireland has high-quality coastal waters in general. 96% of bathing sites in Northern Ireland met water quality standards in 2023, according to the Department of Agriculture, Environment and Rural Affairs (DAERA) bathing water programme.

Of the 26 identified bathing waters monitored, 18 were classified as Excellent, six were classified as Good, one was classified as Sufficient and one failed to meet the minimum standards.

Swim NI helps to protect swimmers against short-term pollution events at sites that might otherwise have high-quality bathing water. 


For any enquiries, please get in touch.