IMPERIAL BEACH, California — Four Mexican citizens were processed Monday after they were seen swimming around the international boundary before landing at Border Field Park in Imperial Beach, officials said.

They were part of a group of 11 that Border Patrol agents from the San Diego Sector observed as they were swimming north from the boundary, according to a U.S. Customs and Border Protection news release.

When the Imperial Beach Station was notified, agents attempted to make contact with the swimmers in an effort to get them to exit the water.

Seven of the people returned to Mexico while the other four kept traveling north, the agency said. They later were captured after they exited the ocean and ran eastbound into the park.

In a statement, San Diego Sector Chief Patrol Agent Aaron Heitke noted that attempts to swim around the border are “extremely dangerous.”

“Smugglers do not care about the lives they are endangering, they will make them swim at night, ill-equipped for the frigid temperatures and without flotation devices or safety equipment,” Heitke said.

No medical attention was required for the four people, who were determined by the agency to be in the U.S. without legal permission.

Further details about the incident were not shared.