SKALA SIKAMINEAS, Greece — The first dinghy landed 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.