Arrests of migrants caught crossing the Mexican border declined in October for the third straight month, the Biden administration said this week.

Border Patrol agents made 158,575 arrests last month, a nearly 15% decline from September. Arrests at the border have declined about 21% since hitting a monthly record in July, when agents made nearly 201,000 arrests, according to Customs and Border Protection data released this week.

Arrests...

Arrests of migrants caught crossing the Mexican border declined in October for the third straight month, the Biden administration said this week.

Border Patrol agents made 158,575 arrests last month, a nearly 15% decline from September. Arrests at the border have declined about 21% since hitting a monthly record in July, when agents made nearly 201,000 arrests, according to Customs and Border Protection data released this week.

Arrests at the border remain high following a record of roughly 1.66 million arrests during the government’s 2021 budget year that ended in September. Arrests last month were more than double those during the same period a year ago.

Border Patrol recorded a 94% drop in arrests of Haitian migrants, a month after more than 15,000 such migrants crossed the border in Del Rio, Texas, and formed a makeshift camp under an international bridge. Last month, agents made 1,083 arrests of Haitians, compared with nearly 18,000 in September. In Del Rio, agents made 116 arrests of Haitians in October.

The drop in arrests of Haitians came after the administration in September renewed removal flights to Haiti, sending back thousands of people who crossed in Del Rio.

Border cities like Brownsville, Texas, are seeing their resources stretched as they work to manage the growing number of migrant families crossing the U.S.-Mexico border. WSJ’s Michelle Hackman reports. Photo: Verónica G. Cárdenas The Wall Street Journal Interactive Edition

Arrests at the border have soared during much of the first year of the Biden administration, overwhelming immigration authorities. The administration says the surge has limited its efforts to roll back many of the Trump administration’s border policies, including the use of a public-health law to quickly turn back the majority of border crossers during the Covid-19 pandemic.

Immigration advocates and others have called on the administration to end the expulsion practice and are suing to block removals. Administration officials have maintained the rule is a necessary public-health measure during the pandemic.

In October, about 58% of border crossers were turned back to Mexico or their home country under the public-health policy, known as Title 42. Most of those turnbacks involved single adults. Single adults accounted for two-thirds of all arrests last month.

The Biden administration is also facing a court order to revive the Trump-era Migrant Protection Protocols, which required asylum-seeking migrants to wait in Mexico for a U.S. immigration court to decide their case. The administration early this month introduced a new effort to end the program, but officials have said in court filings that the government is continuing to work with Mexico to relaunch the program while the new cancellation effort is litigated.

—Tarini Parti contributed to this article.

Write to Alicia A. Caldwell at Alicia.Caldwell@wsj.com