A bison crosses a road ahead of a herd of snowmobilers in Yellowstone National Park in 2003. New federal rules announced Tuesday will further restrict the noise and exhaust such vehicles are allowed to emit inside the park.
Kayakers head out on the Rio Grande toward one of the international bridges that connect Laredo, Texas, and the town of Nuevo Laredo in Mexico. Raw sewage and animal carcasses float in the water.
Neena Satija/Texas Tribune