What does a rainbow sheen on water surfaces typically indicate?

A rainbow sheen on water surfaces is typically indicative of the presence of oil or hazardous materials. This phenomenon occurs because oil is less dense than water, allowing it to spread and form a thin film on the surface. When light interacts with this film, it causes interference patterns that produce a colorful, rainbow-like appearance. This is often a visual cue for environmental scientists, law enforcement, and first responders to recognize potential contamination, prompting appropriate investigation or cleanup actions. It is essential for safety and environmental protection to identify and mitigate the risks posed by these hazardous substances.