1,200 tons of fish washed up on a Japanese beach and nobody knows why

• About 1,200 tons of fish washed up on a beach in Hakodate, Japan, per AP.
• City officials said in a statement that the cause was still unknown.
• The fish may have been chased by bigger fish and died of suffocation, one researcher told AP.

An estimated 1,200 tons of fish have washed ashore on a Japanese beach — and local officials are struggling to explain why.

According to the Associated Press, the volume of sardines and mackerel found floating off the city of Hakodate, in the northernmost of Japan's main islands, was such that it extended across more than 0.6 miles, per officials.

Takashi Fujioka, a researcher at Hakodate Fisheries Research Institute, said it was the first time he had observed such a phenomenon, per AP.

Fujioka speculated that the fish might have been chased by bigger fish, run out of oxygen while swimming together, and then been carried away by the waves.

"We don't know for sure under what circumstances these fish were washed up, so I do not recommend" eating them, Fujioka said, per AP.

In a statement released last week, the city of Hakodate said the cause of the incident remained unknown, but it urged the local population not to bring any of the fish home with them.

The city did not immediately respond to BI's request for comment.

This is not the first time such an event has occurred.

In 2019, thousands of fish washed up in the seaside resort of Hove, in southern England, per the local newspaper Argus.

That same year, California experienced a similar phenomenon, with thousands of Urechis caupo, also commonly known as "penis fish," washing up on Drakes Beach, about 50 miles north of San Francisco, per the BBC.

A year later, thousands of fish washed up dead on the shores of Barmouth, Wales, as ITV News reported at the time.

And in June 2023, tens of thousands of dead fish washed up on the shores of Texas's Gulf Coast. This was due to a lack of oxygen in the water resulting from a rise in temperature, Quintana Beach County Park said in a statement on Facebook.

A lack of oxygen can be caused by several factors, including excessive water extraction by farms, higher temperatures, nutrient overload, and poisoned water, experts told National Geographic.

To stop further incidents of this kind, the experts said, there needs to be policing of what humans dump into lakes and rivers, as well as limiting the amount of water humans pull out of them.

Another priority needs to be intensifying the fight against climate change, including the extraction of fossil fuels, so that maritime heatwaves become less common, they said.