What physical indicator is commonly associated with chemical spills in water?

The presence of a rainbow sheen on water surfaces is a commonly recognized indicator of chemical spills in aquatic environments. This sheen occurs due to the physical and chemical properties of certain pollutants, particularly hydrocarbons and other organic compounds, which can create a thin film on the water's surface. As light refracts through this film, it creates a spectrum of colors resembling a rainbow.

This phenomenon not only signifies contamination but also can suggest the type of chemicals involved, helping responders to identify the potential hazards associated with the spill. Monitoring for such visual signs is a critical part of assessing water quality and implementing appropriate response measures to mitigate environmental impact.