The deaths of at least nine migrants in the Rio Grande River as they tried to cross the U.S.-Mexico border marks the latest tragedy that highlights the risks facing those seeking to illegally enter the United States.

Customs and Border Protection (CBP) said Saturday that the death toll in the incident had risen to nine. The bodies of eight migrants were found Thursday, after Border Patrol in Del Rio Sector responded to reports of a large group of people.

An additional 53 migrants were apprehended, 37 of whom were rescued as they tried to cross the river.

Two of the dead were found by Mexican authorities and another six by American agents, CBP had said on Friday. Across the river, Mexican authorities took into custody another 39 people.