The correct answer is: runoff.

Why runoff is the answer

  • Runoff is water that flows over the land surface after rain or snowmelt, picking up pollutants like soil, oil, fertilizers, pesticides, and trash as it moves.
  • Because it is moving across the ground, it can easily become polluted before it reaches streams, rivers, lakes, or oceans.

Why the other choices are not correct

  • Ponds are standing bodies of water; they can be polluted, but they do not “travel over land.”
  • Groundwater is water stored underground in soil and rock; it moves slowly through the ground, not over the land surface.
  • Oceans are large, mostly stationary bodies of salt water; they receive polluted runoff, but they themselves do not “travel over land.”

So, among ponds, groundwater, oceans, and runoff, the water source that may become polluted as it travels over land is runoff.

Information gathered from public forums or data available on the internet and portrayed here.