With Greece fearing Turkey will let human traffickers accelerate their actions, another 300 refugees and migrants landed on the already-overrun Aegean island of Lesbos, which is housing thousand in an overcrowded detention center.

As part of a suspended swap deal with the European Union – which is ready to release another 3 billion euros ($3.7 billion) to Turkey to deal with three million refugees and migrants, most fleeing Syria’s civil war – Turkey is supposed to take back those who do not receive asylum in Greece, but only a relative handful have been returned.

Greek islands are already awash in more than 15,000 of them, as well as nearly another 50,000 on the mainland and as human rights groups have constantly complained about unfit conditions in detention centers and camps.

Greece fears Turkish President Recep Tayyip Erdogan, stepping up provocations in the Aegean, will unleash more on the Greek islands and that warmer weather will encourage more to try to reach Greece’s islands as the EU has closed its borders to them.

Eight boats carrying the 300 new arrivals landed on Lesbos in a matter of hours on the night of March 28, the business newspaper Naftemporiki said. There are already more than 5,300 being housed there, with frequent tension and even riots breaking out.

Greek search and rescue units also searched a portion of the Evros river bank – which separates Greece and Turkey – after an emergency call was received by authorities. The caller claimed that 15 people who attempted to illegally enter Greece were stranded along the river, the paper said.