This time last year, migrants from Central America, including thousands of unaccompanied minors, were streaming into the United States, creating a problem for border communities and Obama administration officials. With far fewer people reaching American soil this year, it is tempting to conclude that the crisis is ebbing.

That would be a mistake.

Thousands of desperate Central Americans fleeing violence, poverty and, in some cases, persecution, are continuing to embark on perilous journeys north. A growing share, though, are being turned back at Mexico’s southern border.

“The root causes of migration haven’t gone away,” said Maureen Meyer, an expert on migration trends who has analyzed recent data from immigration authorities in Mexico and the United States. “Things are certainly not getting any better.”

American immigration authorities along the southern border detained more than 70,400 non-Mexican migrants between October and April of this year, a majority of whom are from Central America. That represented a considerable decline from 162,700 detained during the same period 12 months earlier. Meanwhile, Mexican officials stopped nearly 93,000 Central American migrants between October and April of this year, far exceeding the 49,800 detained in the same period 12 months earlier.