The unidentified yellow sponge filled the French beach

Hundreds of thousands of yellow objects that look like sponges appear along the northern coast of France.

Spongy yellow-like strange objects appear along the 30km coastline in Pas-de-Calais area, north of France, last weekend, according to Gizmodo. Local authorities are not sure where they come from and an investigation is underway. Results are expected to be published after a week.

According to Local, this kind of material drifted to some beaches like La Slack, Wimereux, Le Portel, Equihen-Plage, Hardelot, Le Touquet, Stella and Berck. The workers are trying to clean them up. The French authorities say that this phenomenon is not a threat to the public, animal or plant health in the area.

Most likely they are products of oil.

Jonathan Hénicart, president of a coastline non-governmental NGO in France, said contact with sponges should be avoided until accurate research results are available.Most likely they are products of oil.

"Foam blocks on the coast may be a polyurethane product commonly used in construction. They have a very light smell of paraffin , " Hénicart said.

In January 2017, people who took dogs on a walk were warned not to let their pets eat a white substance that was like wax on the coast in Pembrokeshire, Wales. Many people believe that this is palm oil, not dangerous to humans but poisoning dogs if swallowed.

The sponge is a natural product of the ocean. In addition to water and air to form, it also needs a surfactant, a bonding molecule that binds between the surface of the water and the air. Human-generated surfactants such as fertilizers, detergents and waste water.

Sponges of sponges cover the French beach.(Video: Sun).