More than 178,000 immigrants were stopped at the southwest border in April, marking a 21-year high in monthly apprehensions, while the number of migrant children crossing the border without their parents fell by 12 percent, according to new numbers published Tuesday by Customs and Border Protection. The number of monthly encounters was up slightly from March, in which Customs and Border Protection encountered just over 173,000 immigrants crossing into the United States from the border with Mexico. The 21-year high was driven mainly by single adults attempting to cross the border illegally, according to CBP data, the vast majority of which were expelled. The Biden administration is continuing to turn back single adults and many families under an authority enacted by the Centers for Disease Control and Prevention intended to stop the spread of Covid-19.