Migrants wait at a Turkish coast guard station in Izmir’s Dikili district after they were caught while trying to reach the Greek island of Lesbos. (Ozan Kose/AFP/Getty Images)

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 is slowing or that refugees are changing course as Europe scrambles to erect new barriers.

Migration officials and aid workers said that 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 retirees dozing on benches.

Syrian asylum seekers and the smugglers who serve them on the Turkish coast said many migrants were anxious that the European Union was going to make good on its promise to stop the trafficking and turn the refugees back from the islands.

A migrant waits at a coast guard station in Izmir, Turkey, on March 20. (Ozan Kose/AFP/Getty Images)

“I fear Europe is now lost to us,” said Jassem al-Saleh, a Syrian mathematician who fled Damascus four months ago.

Saleh, 32, got stalled in Izmir while he waited for his fiancee to be smuggled over the border from Syria. She tried twice in two months before she succeeded in joining him a week ago. Now the newlyweds may have missed their chance, they say.

Saleh said the couple didn’t want to waste the $600 each to make the risky passage to Greece, if they were only going to be returned to Turkey the next day.

“It’s bad business,” he said. “We’re watching and waiting.”

So the couple spent their honeymoon camped out at a smuggler’s crash pad. They were his only customers.

“For sure, some Syrians will still try the sea,” Saleh said. “They’re risking their lives, so they think the Greeks can’t send them back. But I think they will send them back. I think the deal is done. This way is finished.”

A migrant girl cries as she waits at a coast guard station in Izmir, Turkey on March 20 after being caught with other migrants while trying to reach the Greek island of Lesbos. (Ozan Kose/AFP/Getty Images)

Over the past 15 months, about 1 million refugees were smuggled from Turkey to the Greek islands. The maritime smuggling mafias made more than $4 billion last year, authorities said.

Some 400 people have died in the Aegean Sea crossings. Most of them drowned, according to the Greek coast guard. An additional 170 are listed as missing.

Earlier this month, the E.U. and the Turks closed a deal that envisions both war refugees and economic migrants stopped in the Greek islands that hug the Turkish coast.

The plan calls for those who make it to the islands to be detained and interviewed by immigration officials there. European leaders then want most of the refugees escorted onto ferries and sent back to Turkey.

The E.U.’s Frontex agency, which is responsible for stopping illegal immigration, is bringing the first of 2,500 police officers, asylum case officers, judges and interpreters to Greece to begin processing the refugees.

“We know there is a deal, but we don’t care. We will go, and they will take pity on us,” said Safa Abdulkarim, 40, a widow who is traveling to Belgium, where a new husband awaits her. “A dear friend,” she explained, a Syrian with Belgian citizenship who drives a bus in the city of Leuven.

Abdulkarim said she is strong and the sea does not frighten her. But doubt began to creep into her conversation.

“Can they really just send us back?” she asked. Abdulkarim began to recount a story told by millions of refugees before her — how she fled war and killing in Syria, escaping from Palmyra to Douma to Homs, how she ran across the muddy Turkish border with a smuggler whom she paid $1,800, bringing along her 18-year-old daughter and younger son.

More than 60 percent of the arrivals in the Greek islands are women and children. Half are Syrians; Afghans and Iraqis are the next-largest groups.

Europe has apparently heard enough of these stories and has promised to stop the wave of new arrivals — a decision reached before suicide bombers struck in Brussels last week, possibly stiffening its resolve.

E.U. officials argue that Turkey can provide a safe haven and have vowed to shut down the eastern Mediterranean route.

In exchange for accepting refugees returned from Greece, Turkey gets more than $6 billion in assistance, eased visa requirements for its citizens to travel to Europe and a renewal of negotiations to bring Turkey into the E.U.

Migrants arriving in Greece after March 19 are being taken to “closed” detention facilities on the islands. Greece will no longer let them pass through to the mainland. Frontex officials said the first ferries carrying asylum seekers back to Turkey are expected to set sail April 4, although Greek officials have wondered aloud whether the parties can get the repatriations up and running by then.

Cigdem Elibol, the deputy mayor of the Turkish seaside town of Dikili, where the ferries will land, said authorities are preparing to build a temporary processing center.

She said people in the town felt sorry for those who risk everything at sea, but they also fear their town will be overwhelmed by angry migrants denied their dream.

In Izmir, in the warren of side streets around the Basmane train station, the hotels that last year were packed with guests are now empty.

“Not a soul here,” said the proprietor of the Hotel Ahmet, who was hopeful that business would pick up if the refugees are returned from the Greek islands.

In the Syrian-style barber shops and coffeehouses, the middlemen for the smugglers were hustling for scraps. Hassan, who declined to give his full name because smuggling is illegal in Turkey and who considers himself more of an “organizer for trips” than a human trafficker, said his Turkish bosses are beginning to plan alternative routes to Europe.

One of his colleagues said Romania via the Black Sea was an option. The smugglers said there were rumors that the traffic could pivot again to southern Turkey, where desperate travelers were packed by the hundreds into decommissioned cargo freighters known as “ghost ships,” because the crews set the autopilot for the Italian coast and abandoned the passengers to their fate.

For many of the nearly 3 million Syrian refugees in Turkey, Europe is just too far away now.

“To be honest, we ran out of money. So here we are,” said Mohammad Alawaq, 45, who was putting on his shoes after praying in a mosque next to the train station.

“It’s not so bad,” he said. “The Turks treat us well enough.” He makes a few dollars an hour hauling goods around the central market.

Alawaq said he heard they would start turning back Syrians anyway. “So we will all be stuck here together,” he said.

Read more:

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Today’s coverage from Post correspondents around the world