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Discoloured water on Dublin beaches down to algal bloom, says council

Bathing bans are in place at beaches across Dublin Bay.

Updated Jun 25th 2019, 5:30 PM

BEACH The discoloured water at Sandycove. Source: Flossieandthebeachcombers/Twitter.com

DISCOLOURED WATER SPOTTED at Dublin beaches is due to algal bloom and is not connected to an overflow from a wastewater treatment plant that prompted bathing bans across the bay.

Bathing bans are currently in place at Seapoint, Sandycove and the Forty Foot on Dublin’s southside in addition to Dollymount on the northside. 

Images circulated on social media earlier showed the water at some of the affected beaches had turned orange-brown. 

Dún Laoghaire Rathdown Council has since released a statement saying that the discolouration of the water was not due to the presence of raw sewage, but was instead down to the build up of a micro-alga called noctiluca scintillans.

The council said that this is “non-toxic”. 

A spokesperson said: “Further to reports in media and social media about orange water at Sandycove Beach and immediate surrounds today, we have taken samples of the orange coloured water at Sandycove this morning. Results this afternoon show that this is not raw sewerage but is a micro-alga called noctiluca scintillans. This is a benign, non-toxic, species – the ‘blooms’ are characteristically yellow, orange or orange/red.

The appearance of this algal bloom is not directly associated with the waste water overflows associated with the temporary bathing prohibition. We have been advised that this is a natural summer phenomenon in response to long day length, high nutrients and warm water.

The council said that the presence of the algae had been reported along the east coast for the past few weeks and was typical for this time of the year.

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Further no-swim notices were already in place at Sandymount and Merrion beaches because of poor water quality before the latest bans came into effect.

Confirming the bathing ban at Dollymount yesterday Irish Water said in a statement: 

“Due to adverse weather conditions during a yellow weather warning event, which saw heavy rainfall in the Dublin area, there was a stormwater overflow from Ringsend Wastewater treatment plant. The stormwater overflow operated in compliance with plant design and regulations, and was fully screened and settled.”

About the author:

Daragh Brophy

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