Why Heavy Rain Is Bad News for Swimmers

Grainne Saunders discovers why sea swimming in Dublin Bay isn’t always good for your health.

A nice day for a dip. 

19th June 2020 was the first dry day after a few days of intense thunderstorms.  Ireland is in lockdown but Dubliners lucky enough to live within 2kms of the sea can take advantage of our beautiful sandy beaches.  On Dollymount, Portmarnock, and Sandymount beaches, signs have been erected. Perplexed would-be swimmers, on seeing the sign, wonder how heavy rainfall makes the sea dirty.

The temporary bathing ban notice at Dollymount Strand.

The temporary bathing ban notice at Dollymount Strand. Credit: Beaches.ie

What’s going on at Ringsend Wastewater Treatment Plant?

Everyone knows that the waste from your house goes down the sewers into the pipes is carried to Ringsend is treated and then released into the sea.

But we may not know that the use of combined sewage outlet pipes means that rain that goes into the drains at the side of the roads is also emptied into the same pipe.

So, after heavy rainfall, Ringsend treatment plant must make a decision. They can open the storm water overflows and discharge the untreated excess from the sewer directly into the sea or do nothing and risk the treatment plant becoming inundated and homes and streets being flooded with sewage.

Images were taken from EPA Urban Wastewater Report (Figure 8: Storm water overflow.)

Irish Water advise that by releasing the storm water into the sea that this wastewater is highly diluted with rainwater and has been screened and settled to remove debris. However, they still must notify the EPA (Environmental Protection Agency) and in conjunction with DCC (Dublin City Council) and the HSE (Health Service Executive) take the decision to prohibit bathing, as a precaution. 

Precautionary Notices

The EPA Urban Wastewater report published in November 2020 states that: “A precautionary approach is taken when reporting bathing water pollution incidents, meaning that not all incidents actually result in a deterioration in water quality. This precautionary approach is taken to protect bathers’ health. “

Once the precautionary notice is issued, it cannot be lifted until a second sample is tested. This is frustrating for frequent swimmers like, Green Party Councillor, Donna Cooney, who told me that: “currently testing has to go to a lab and can take 48hrs to 3 days to get a result. Often the water turns out to have been ok during that time, but bathing has been prohibited as they err on the side of caution. What’s worse is when you find out you have been swimming in contaminated water for up to 3 days and didn’t know it.”

Testing of Bathing Water

DCC monitor the bathing water quality and during the 14 weeks of the bathing season from 1 June to 15 September, they take 20 samples.

We need more frequent testing. This is a view shared by local campaigners Save Our Seas who started an online petition calling for the water to be tested daily. So far, they have 18,500 signatures. Their slogan is “heavy rainfall = sewage dump into Dublin Bay.”

Emily Williamson of EPA told me, that during the overflow incident on 17 June (the one that caused the warning notices on the beaches on the 19th) Irish Water notified them that it had discharged 49.8 million litres of untreated waste water. Enough to fill 20 Olympic sized swimming pools.

This was just one of 7 discharges, during the bathing season, of untreated water from Ringsend. Figures supplied in the DCC 2020 Bathing Water Report advise that bathing was prohibited on Dollymount for 5 days in June, 8 days in July and 21 days during August and September.

I asked Irish Water if they could tell me the amounts of untreated wastewater discharged each time, but they could only furnish this information upon receipt of an Access to Information on the Environment Request (AIE).

In 2019, Stephen McDermott of The Journal found out through an AIE request from Irish Water that: “a total of 320 million litres of untreated wastewater was discharged from storm holding tanks at Ringsend over 7 occasions in 2019.” Enough to fill 128 Olympic sized swimming pools.

Photo by Oliver Sju00f6stru00f6m on Pexels.com

Why can’t Ringsend cope?

The Ringsend plant treats approximately 44% of Ireland’s public wastewater, treating the whole of Dublin and parts of Meath. It has a capacity to treat wastewater for approximately 1.64 million people, but there are approximately 2 to 2.4 million users.

The capacity is not big enough, even before it rains, and it is failing to meet national and EU treatment standards.

What is Irish Water doing to fix it?

Irish Water stated that work on the plant to add capacity for an extra 400,000 population would be completed in 2021. Forecasted works to expand capacity to support the 2.4 million population will be completed by 2025.

In the meantime, they are proposing an investment of €500 million to build another treatment plant to relieve pressure on Ringsend. The new plant would be in Clonshaugh in north Dublin. It would take wastewater from the Blanchardstown area, treat it in Clonshaugh and then pipe it to the coast. The pipe would enter the sea near Baldoyle and continue out beyond Ireland’s Eye where the treated wastewater would be discharged.

Planning permission was granted but following a successful appeal in November 2020 by Portmarnock residents the permission was overturned.

What is the government doing?

Minister for Housing, Darragh O’Brien met with Irish Water in November following the release of the EPA report. The minister has cleared €100 million extra for Irish Water capital spending. As he said to Kevin O’Sullivan in the Irish Times: “I am committed to giving funding so projects can proceed and catch up if they need to.”

A new type of testing – 

Donna Cooney says: “The testing period should be extended as more people are now swimming all year round. Testing should be done every day, even a quick test will give an indication.”

In the summer of 2021, Irish Water confirmed that they will expand the testing of water quality in Dublin Bay beyond the traditional bathing season. 

Ruth Clinton, water innovation officer at the Water Institute – Dublin City University (DCU), told me that to manage the bathing areas and inform the public quickly of the presence of “faecal pollution” they had developed: “a rapid on-site test for E. coli detection and successfully tried and tested on environmental water samples. This test has a time-to-result of less than 75 min.”

The results of this on-site assessment of water quality could work in tandem with the current alert systems and give an early indication of pollution. 

Clinton, advised: “that the technology is at an early stage of development and that they are currently applying for funding to develop it further.”

Can’t get into the sea but what about the beach?

Donna Cooney says “people often don’t realise that when the tide goes out the sand left behind is contaminated and could pose a health risk to kids playing in the sand, pregnant women, people with immune deficiency, and pets.”

Written by – Grainne Saunders

What to know about the water quality at your local beach? Click here



Thank you to Donna Cooney, Green Party Councillor for the interview.

Thank you to Stephen McDermott of The Journal for allowing me to use your information and for your advice about AIE requests.

Thanks to The Sun Newspaper for the Warning Notice.

You can check out Irish Water here.

You can get information on the work of the Environmental Protection Agency here.

DCU Water Institute to find out about the development of the new test.

EPA Urban Wastewater Report to check out the latest reports.


Questions to consider? 

Are you a sea swimmer in Dublin? 

Were you aware of the potential dangers highlighted in the article in terms of sea swimming, at Dublin Bay? 

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