When Brent Rossenpostedhis girlfriend's photo of a rainbow swamp on Reddit, it received more than 120,000 upvotes in 24 hours.
"Me and my girlfriend were walking in the woods the other week and saw a rainbow pool for the first time" his post read.
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."
Jeff explained that the water needs to be still for long periods in order for the rainbows to appear.
"Movement by sheet flow, current or wind disturbance would destroy the fragile rainbow film," he said.
He added that he normally sees the phenomenon in smaller areas.