Long jams developed on some Dutch coastal roads in Zeeland and Noord-Holland on Monday as holidaymakers tried to avoid beaches which have been hit by red algae blooms.

The algae has been identified as Noctiluca scintillans, commonly known as the sea sparkle, broadcaster Nos said on Monday. Although not toxic, this large single cell plankton can cause skin irritations.

Sea sparkle is common in shallow sea areas and produces bioluminescence when disturbed.

Swimming was banned in the stretch of North Sea between the resorts of Katwijk and Scheveningen until the exact type of algae was identified.

Beach goers are still being recommended to avoid the beaches where the red bloom has been spotted. ‘We think it better that people don’t go in the water,’ a spokesman for the national water authority told news agency ANP.

Monday is one of the hottest days of the year, with temperatures expected to reach 28 degrees on the coast.