Red flags along some of the Netherlands most popular North Sea beaches were taken down on Monday afternoon after government officials said the algae bloom had disappeared.

A stretch of beach between Scheveningen and Katwijk was closed on Sunday while experts tried to determine what had caused the red clouds in the sea.

Long jams developed on some Dutch coastal roads in Zeeland and Noord-Holland on Monday as holidaymakers tried to avoid beaches where swimming had been banned.

The algae was later identified as Noctiluca scintillans, commonly known as the sea sparkle. Although not toxic, this large single cell plankton can cause skin irritations.

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