What warnings does Enrique get when he reaches the Rio Grande?

From the text:

They tell him the trek is treacherous from the moment you step into the river. A month ago, one of the camp dwellers saw a man’s body float past. It was bloated. Sometimes, friends say, migrants are killed when whirlpools suck them under. Other times, whirlpools smash their heads against rocks. Sometimes their legs cramp and they sink. Other times INS helicopters fly too low, whip up waves, and swamp inner tubes, riders and all. They call the helicopters mosquitoes; they come down and bite.