Officials reported on Friday that an unknown cause has resulted in the beach in northern Japan being littered with thousands of tons of deceased sardines.

On Thursday morning, a large number of sardines and mackerel were found on the shore in Hakodate, located on the northernmost main island of Hokkaido in Japan. The fish covered about a kilometer of beach, creating a shiny layer of silver.

The locals claimed they had never witnessed such a spectacle before. A few of them collected the fish to either sell or consume.

The city advised its citizens, through a notice on its website, to avoid consuming the fish.

According to researcher Takashi Fujioka from the Hakodate Fisheries Research Institute, he has previously been aware of similar occurrences, but this was his first experience witnessing it.

According to him, the fish could have been pursued by bigger fish, experienced fatigue from insufficient oxygen while swimming in a crowded group, and then were carried onto shore by the waves.

According to him, the fish may have unexpectedly encountered cold waters while migrating.

According to him, the decaying fish may decrease the oxygen levels in the water and impact the marine ecosystem.

Fujioka stated that due to the unknown circumstances surrounding the washing up of these fish, it is not advisable to consume them.