Authorities rescued 91 migrants from a river islet and transferred them to a processing center near the border with Turkey, police said Sunday.

The migrants had been on an islet on Evros River at least since Friday, when nongovernmental organizations emailed Greek authorities alerting them to their presence there. Part of the islet is Greek soil and part is Turkish. By early Sunday, the migrants had moved to the Greek side, enabling the rescue operation, a statement from the prime minister’s office said.

The river’s low water levels of late “favors the illegal crossing of migrants, using islets that fall on both Greek and Turkish territory … the Greek government has appealed to the Turkish government, which was sworn in (Saturday), to coordinate border authorities and prevent illegal crossings,” the statement added.