20/07/2017 12:41 BST | Updated 20/07/2017 12:57 BST

Mystery As Millions Of Yellow Sponges Wash Up On French Beaches

Curiouser and curiouser.

Close to 20 miles of idyllic French coastline has been colonised by millions of mystery yellow sponges.

The Local cited authorities confirming on Monday that while they were not sure where they came from, “to their knowledge”, the sponges are not a danger to “public health, animals or plants” in the area.

Jonathan Hénicart, president of Sea-Mer a French non-profit organisation that fights beach pollution, told French TV news channel BFMTV: “It seems to come from an oil product. It could come from a polyurethane product commonly used for building. And it smells very, very lightly of paraffin.”

The sponges have landed on the English Channel coastline of France's northern Pas-de-Calais department

The beaches affected are La Slack, Wimereux, Le Portel, Equihen-Plage, Hardelot, Le Touquet, Stella and Berck, French daily La Voix du Nord reports. 

There have been suggestions the strange substance could be sea foam, a naturally occurring phenomenon that can occur after big storms or cyclones when wind or waves stir the ocean, mixing up the salt water’s proteins, dead algae and other tiny particles.

The substance is currently being analysed 

But Gizmodo points out: “in addition to needing air and water to form, it also needs a surfactant —a binding molecule that clings to the surface between water and air.”

It adds: “Surfactants can come from many human-caused sources, including fertilizers, detergents, and sewage. Some kind of chemical with this binding property may be churning in the waters near the Pas-de-Calais, but we’re going to have to wait a few days to find out exactly what it is.”

Tests are currently being conducted on the strange substance and the beaches are being cleaned.