Japanese shores witness the puzzling phenomenon of hundreds of tons of fish washing ashore, leaving officials in a quandary over the cause.

Earlier this month, the coastal town of Hakodate in Hokkaido was met with an astonishing sight as an estimated 1,200 tonnes of sardines and mackerel formed a silver blanket stretching over a kilometer on the sea’s surface. The spectacle left local officials bewildered, unable to ascertain the reason behind the massive fish wash-up.

This enigma escalated when, on Wednesday, the town of Nakiri, situated hundreds of miles south of Hokkaido on the Pacific coast, grappled with 30 to 40 tonnes of Japanese scaled sardines, locally known as sappa. Fearful of the potential damage to the marine environment due to decomposing fish lowering oxygen levels in the water, local fishers rushed to collect the stranded fish.

“I’ve never seen anything like this before,” remarked a veteran fisher with 25 years of experience in the area. Concerns were raised about potential shifts in the marine ecosystem, given that sappa catches in Nakiri had only started around a year ago.

While experts speculated that the fish might have become stranded after exhausting migratory pursuits or due to sudden drops in water temperature, the exact cause remains elusive. Mikine Fujiwara, a local fisheries official, stated, “The cause is unknown at the moment. We plan to sample the seawater at the site and examine it to uncover the cause.”

A controversial report from the Daily Mail linking the fish wash-up to the release of treated water from the Fukushima Daiichi nuclear power plant faced strong rebuke from Japanese government officials. The report suggested a correlation between the phenomenon and the discharge of water containing small amounts of the radioactive isotope tritium into the Pacific. The International Atomic Energy Agency had previously approved the plan, assuring minimal radiological impact.

Japanese fisheries officials expressed concern about “unsubstantiated information” and emphasized the lack of abnormalities in water-monitoring surveys related to the Fukushima plant’s discharged water. China, opposing the release, has been accused of hypocrisy, given its own nuclear plants’ higher tritium levels in wastewater.

As images of the stranded fish circulate on social media, conspiracy theories related to Fukushima gain traction. The Japanese fisheries agency urges caution, emphasizing the absence of scientific evidence supporting these claims. Fishing cooperatives in Fukushima had previously warned about the potential damage to the reputation of their seafood due to the water discharge.

Local authorities in Hakodate issued warnings against consuming the stranded fish, urging residents to refrain from selling or consuming them due to uncertainties surrounding their wash-up. “We don’t know for sure under what circumstances these fish were washed up, so I don’t recommend eating them,” said Takashi Fujioka, a fisheries researcher.