Mission, Texas — Border patrol agents have a hard enough time keeping undocumented immigrants and smugglers from crossing a bridge here — through a 96-acre park that lies on the border with Mexico — without having to worry about what might be going on in the water below.

Ten minutes was all the time needed for a man to jump on a jet ski in Mexico, cross the Rio Grande River into Anzalduas County Park and hop in car that nonchalantly bypassed police vehicles and park gates. The man was part of a team of at least 4 who scoured the area before his departure and helped the jet skier mount the vehicle without ever getting his feet wet.

Park police said they see about 12 "jet ski jumpers" cross into the park daily, and only 40 percent of them are caught. Sgt. Dan Broyles, who patrols Anzalduas County Park, said his job has never been easy, but recently, "it's like digging a hole and throwing all of the dirt up a hill."

Broyles said he feels like he is "on the front lines in a non-violent invasion," as 1,200 people cross this strip of the Rio Grande every day, including up to 400 unaccompanied children.

Last Saturday, NBC News crews encountered a total of 17 Salvadorans, including children, who had just crossed into the US. They first asked for water. Then they inquired what country they were in, fearing they were still in Mexico.

The number of unaccompanied minors at the southern border has soared more than 1,000 percent amid rampant crime and poverty in Central America, according to Border Patrol data. Already this year, border agents have apprehended some 47,000 children entering the United States via Mexico from Guatemala, El Salvador, and Honduras.

President Barack Obama has called the surge a crisis.

Homeland Security Secretary Jeh Johnson has said that the wave of children arriving from Central America was a "problem of humanitarian proportions."