Surface water is bodies of water, like oceans, lakes, streams, or water springs.

Surface water contamination occurs when hazardous substances dissolve or mix with the water bodies. Because of the close relationship between sediments and surface water, contaminated sediments are often considered part of surface water contamination. Sediments include the sand and soils on the bottom of an ocean, lake, or stream.

Surface water can be contaminated when hazardous substances flow from an outfall pipe or channel or by mixing with contaminated storm water runoff ( see the animation below ). Direct discharges can come from industrial sources or from some older sewer systems that overflow during wet weather.

Storm water runoff becomes contaminated when rain water mixes with contaminated soil and either dissolves the contamination held in the soil or carries contaminated soil particles.

Surface water can be contaminated when contaminated groundwater reaches the surface through a spring, or when airborne contaminants fall onto the surface water. Contaminated soil particles carried by storm water runoff or contaminants from the air can sink to the bottom of a surface water body, mix with the sediment, and remain.