This white foam seen covering a Russian river has led the authorities to look into its origin after reports of someone dumping a substance into the river shortly before it appeared.

The bizarre white foam substance was seen over the Volkovka River in the Russian city of St Petersburg.

Locals had shared images of the strange scene on their social media before it was reported by local sources earlier this week.

The videos show some of the footage capturing the strange white foam which can be seen covering the top of the entire canal which stretches a long distance.

Local media said the authorities sent experts to investigate the substance but there have been no further reports on what it could be or how it got there.

An unnamed netizen posted images of the thick layer of foam covering the water on the social media page ‘Accidents and Emergencies St Petersburg’.

The netizen left a caption that read: “Someone periodically pours foam waste into the Volkovka River.” However, no further information was given.

Online Russian newspaper DP said officials told them they “were already aware of the situation” adding: “We have information they are already working in the area.”

The same report added the same foam had appeared in the Duderhof Channel in St Petersburg which accumulated so much it interrupted traffic but no further information was given.