SKALA SIKAMINEAS, Greece — The first dinghy landed at about 5:45 p.m., on a rocky shore near a remote Greek fishing village. After the thirteenth arrived about 35 minutes later, 547 migrants had landed, in broad daylight, within a few yards of each other on the Greek island of Lesbos.
That flotilla on Aug. 29 repeated a pattern not seen here since early 2016, when the European Union pledged more than $6 billion to Turkey, which lies within view of Lesbos, to tighten its border patrols and keep migrants out of Europe.
In the years since, only one or two refugee boats have typically made it to this stretch of Greek coast each day, substantially easing Europe’s migration crisis. But that rhythm changed this August, the busiest month in more than three years, feeding fears of a new wave of mass migration across the Aegean Sea.
The rate of arrivals is still just a fraction of the 2015 peak, when Lesbos was the busiest European entry point for migrants — primarily people fleeing the Syrian civil war. Last month, nearly 10,000 migrants arrived in all of Greece; in October 2015, at the height of the crisis, more than 210,000 did.
But the recent surge comes as President Recep Tayyip Erdogan of Turkey threatens once again to allow high numbers of migrants to make their way through Turkey to Greece, should European politicians fail to provide Turkey with further financial support, or dismiss his plans to extend Turkish influence in northern Syria.
“This either happens,” Mr. Erdogan said in a speech last week, “or otherwise we will have to open the gates.”
The August increase shows this may not be an idle threat. But if he intends to create a new refugee crisis for Europe, Mr. Erdogan has fewer tools to work with than he did in 2015, when Syrian refugees found it easier to enter Turkey.
Turkey has since completed a border wall and has imposed restrictions on Syrians traveling from Lebanon or Jordan. Any relaxation of those controls, admitting more people — even if only to use Turkey as a bridge to Europe — would be politically risky for Mr. Erdogan.
But 3.6 million Syrian refugees already live in Turkey, the world’s largest expatriate Syrian population, along with hundreds of thousands from other countries. If Turkey makes life untenable for them, or relaxes efforts to keep them out of Europe, the effect could be dramatic.
“Erdogan’s recent comments on unleashing a new refugee wave are a product of his growing frustration with the huge number already in Turkey,” said Bulent Aliriza, director of the Turkey project at the Center for Strategic and International Studies, a Washington-based research group.
“It is unlikely that there is a fully thought-through master plan ready for implementation,” he added.
The fact that Turkish smugglers were able to gather so many people on Aug. 29 and send them to Greece in such quick succession has raised questions about Turkish state complicity.
Turkey’s Coast Guard, normally fairly active in these waters, did not respond that afternoon to repeated requests for intervention by their Greek counterparts, according to Refugee Rescue, a small private lifeboat organization that helps stricken migrants and has access to maritime communications.
Turkish vessels also stuck to a pattern of morning patrols throughout August, even as smugglers repeatedly sent refugees to Greece in the afternoon.
“What we found weird was that this was a trend, and they didn’t change the way they operated to try to stop this,” said Finn Sands-Robinson, who leads Refugee Rescue’s land-based observation team.
A senior Turkish official, who insisted that his name not be used, denied that Turkish authorities had turned a blind eye to smugglers.
Mr. Erdogan’s government stepped up the deportation of Syrians from Turkey this summer, and it was widely assumed that this crackdown caused the rise in departures to Greece.
But more than 80 percent of the migrants who landed in Lesbos in August were from Afghanistan. Increasingly precarious conditions in Turkey and Iran, where at least a million Afghans live in exile, as well as in Afghanistan itself, have led many Afghan refugees to head for Europe.
Gholam Reza Salahi, a 25-year-old Afghan laborer who has lived most of his life in Iran, said he decided to go to Greece after being deported for the fourth time from Iran to Afghanistan.
“We’d be smuggled back to Iran, and then deported again,” he said. “And that happened too many times.”
As a member of the Hazara ethnic group, who are persecuted by the Taliban, he felt he could not stay in his parents’ country. Nor did Turkey feel like a plausible sanctuary: Ankara has deported 32,000 Afghans so far this year, far more than any other national group.
Europe felt like the safest bet, said Mr. Reza Salahi, who reached Lesbos in late August.
Just 5 percent of migrants arriving in Lesbos last month were from Syria, suggesting that few Syrians yet feel anxious enough to leave Turkey. But the testimonies of new Syrian arrivals provide a hint of what might be to come.
A group of families from northern Syria, huddled in a tent on a Greek hillside, had for seven years refused to flee their neighborhood despite regular air raids, the destruction of their homes and schools, and the deaths of many relatives and friends.
But this summer, they finally decided to leave Jabal al-Zawiya, a rebel stronghold, because of a sharp escalation in airstrikes and the likely recapture of the area by President Bashar al-Assad’s forces.
“The Assad army, when they take a place, they burn it,” said Obeida al-Nassouh, a shopkeeper who said he had paid $3,500 for his family to be smuggled through a secret tunnel to Turkey, and then onward to Lesbos. “They don’t care if you’re a civilian or a soldier, they just burn it.”
Fighting has intensified in Idlib, a Syrian province bordering Turkey, prompting more people to try to leave.
The enormous number of Syrians already in Turkey provokes considerable resentment within Mr. Erdogan’s political base, and he is keen to cut the refugee population.
Youssef al-Hassan, 44, a recent arrival to Lesbos, had for seven years been content to stay in Turkey, where his family lived in poverty but at least felt safe from Mr. Assad’s forces.
But this summer’s deportations of Syrians persuaded Mr. al-Hassan that even Turkey was no longer safe.
“We felt like in the next five minutes they could come and throw us out,” he said a few hours after landing in Greece. “The situation is such that many are going to come.”
True or not, even a small increase in arrivals compounds the misery of refugees in Greece.
In 2015, new arrivals could move swiftly toward the Greek mainland, and then onward to Germany. But today, migrants are contained on the Greek islands, mostly in overcrowded and squalid camps that seem out of place on the world’s richest continent.
On Lesbos, about 10,000 people have been crammed into Moria, a camp built for just 3,100. Though the European Union has allocated around $1.9 billion to the Greek government to subsidize refugee welfare, Greece has refused to improve the facilities for fear of encouraging more migrants.
Residents here sometimes spend up to year living in tattered tents, and up to 12 hours a day waiting in line for food, which often runs out before everyone is served.
“Every day we queue for hours and they say: ‘There’s nothing left,’ ,” said Reza Salahi. “And that’s the case for about a quarter of us.”
Raw sewage sometimes leaks into tents, while fights and sexual assaults are a regular occurrence. Overwhelmed medical workers struggle to treat a soaring number of patients.
Coupled with seemingly interminable asylum procedures, all this has created what aid workers see as a mental health crisis among refugees on the island. Since July, the number of children with severe mental health issues has more than doubled to 73, according to Doctors Without Borders.
An Afghan mother, Sohaila Hajizadeh, who fled to Greece after the Taliban attacked her family’s home, said she had frequently been turned away by doctors when seeking treatment for her teenage son, who has severe psychological trauma. From wrist to shoulder, the boy’s arms are covered in self-inflicted knife wounds.
Unaccompanied children are particularly at risk. Officially, there are 747 refugee children on Lesbos, living without their parents, and provided with secure accommodation by the authorities. But poor registration processes mean that there are more parentless children living undocumented in the camp.
One such youth, Mohammed al-Othman, 16, lives in a cramped tent, together with 12 other people from his home province in Syria. He left Syria in August after his school was bombed; his mother had only enough money to smuggle one family member, so Mohammed went alone.
Since arriving in Greece, he has not received treatment for four shrapnel wounds sustained during a recent airstrike.
“The treatment is very bad,” he said. “They just asked me: How old are you, are you ill? And they left me outside.”
He wore a shirt marked with the slogan: “Grow up.”
The words had been crossed out.