The number of migrants risking the perilous voyage from Turkey to Greece via the Aegean Sea has plummeted, according to new figures released by the United Nations, a sign that a deal brokered by the European Union in March to ease the migration crisis has shown some success.

Under the deal, asylum seekers who use illegal routes to reach the Greek islands from Turkey are being sent back. Turkey is set to receive about $6.6 billion in aid to help the migrants there, many of them from Syria. In return, the European Union will resume negotiations over Turkey’s application to join the 28-nation bloc, and will resettle one Syrian from a camp in Turkey in exchange for each Syrian who is sent back to Turkey.

The complicated deal took effect in April, and it appears to be working, insofar as numbers are concerned.

In June, 1,488 migrants arrived in Greece by crossing the sea from Turkey, down from 31,318 in June 2015; in May, 1,721 arrived, down from 17,889 in May 2015; and in April, 3,650 arrived, down from 13,556 in April 2015. At the peak of the crisis, in October, 211,663 migrants reached Greece via sea routes in a single month. In the first few days of July, only a few dozen migrants have arrived.