"Rainbow swamp" caused by natural oils on water

This photo, taken by Allison Goz, was posted to Reddit by her boyfriend, Brent Rossen. They were curious about why the swamp was rainbow-colored. The BBC reports:
The couple were walking at First Landing State Park, Virginia, US, when they saw the unusual natural phenomenon.
Jeff Ripple, a former Florida swamp walk leader, told the BBC: 'The rainbow sheens found as a thin film on top of pooled water in swamps and marshes are the result of natural oils released by decaying vegetation or the biological processes of anaerobic bacteria reducing iron in soil.