The once great wave of refugees motoring in cheap rubber rafts across the Aegean Sea from Turkey to the Greek islands has suddenly become a ripple.

Where thousands arrived in a day, now hundreds — and some days far fewer — splash onto the Greek shores from Turkey, a possible sign that the largest mass migration of the 21st century may be slowing or that refugees are changing course as Europe scrambles to erect new barriers.

Migration officials and aid workers said rough seas in recent days may be responsible for the dramatic reduction, and that the pebble beaches of Lesbos, Chios and Samos could again see hundreds of boats a day arriving as they did earlier this year.

But in the Syrian quarter of Izmir, once teeming with refugees shopping for life preservers, the cheap hotels are empty. No one is sleeping in the courtyards of the mosques; the dusty parks have been returned to pensioners dozing on benches.