Japan has a lot of uninhabited islands, about 158 of which the government named in 2014 to ensure that the water around them continues to belong to Japan.

But now, one of those islets has disappeared, Japanese newspaper Asahi Shimbun reported this week. And no one seemed to notice until now.

The Japanese Coast Guard is apparently planning to search for the islet, called Esanbehanakitakojima, about one-third of a mile away from Sarufutsu, a village on Hokkaido island.

Hiroshi Shimizu, an author who published a picture book about Japanese islands, was the one who reported that the islet wasn’t where it’s supposed to be. He wanted to visit Esanbehanakitakojima as part of a follow-up book project, but the Japanese newspaper reported that he just couldn’t find it. That’s when he reached out to Sarufutsu’s village fishery to ask where it might be.

It turns out the Japanese Coast Guard had last surveyed the islet in 1987, and it was known to be around 4½ feet above sea level.

But now it can’t be seen from land at all.

“There is a possibility that the islet has been eroded by wind and snow and, as a result, disappeared,” senior coast guard official Tomoo Fujii told the Asahi Shimbun newspaper.

A coast guard official also told Agence France-Presse that the disappearance “may affect Japan’s territorial waters a tiny bit … if you conduct precision surveys.”

Land disappearances are not unheard of. A study published in Environmental Research Letters in 2016, for example, found that five reef islands in the Pacific Ocean’s Solomon Islands had disappeared between 1947 and 2014. That study determined that although sea-level rise has caused erosion in the central Pacific, research in the western Pacific found that “extreme events, seawalls and inappropriate development” likely were responsible for the majority of shoreline changes in that region.

For its part, Japan has taken measures to ensure it lays claim to certain islands to avoid further territorial disputes with its neighbors.

In 2016, Japan announced it would spend $107 million to rebuild the observatory tower on a Pacific island called Okinotorishima, which is about 1,000 miles south of the capital Tokyo.

The Guardian reported at the time that Beijing had claimed the island was made of only rocks and thus disqualified Japan from including it in its exclusive economic zone.

A United Nations convention claimed that “rocks which cannot sustain human habitation or economic life of their own” don’t qualify for such a zone.