Marsh Rainbow Arch Bridge, Concrete road bridge in Iowa, United States.

Marsh Rainbow Arch Bridge is a 271-foot (83 m) three-span concrete bridge over the North Raccoon River south of Lake City, Iowa. Each span has two curved ribs above the deck, connected by vertical hangers, forming the patented rainbow arch profile. It carried Iberia Avenue traffic until 1985 and now stands in a county park.

Designed by Des Moines engineer James Barney Marsh in his patented rainbow arch form, the bridge was built by the Iowa Bridge Company in 1914 for $10,970. It replaced a Howe truss bridge erected by the King Bridge Company of Cleveland, which was moved upstream and served until 1983. The Marsh bridge carried Iberia Avenue traffic until it was bypassed in 1985, and it was listed on the National Register of Historic Places in 1989.

The bridge is now part of a county park at Rainbow Bend Access, south of Lake City, where it stands beside the North Raccoon River. A model of the structure is displayed at The Big Treehouse, a campground attraction nearby. The span is also recorded in the Historic American Engineering Record in Iowa.

The bridge no longer carries vehicle traffic and is preserved as a historical site, so visitors can view it from ground level or nearby. The best perspective is from the side, where you can see the distinctive arch form and the structural details.

A scale model of the bridge stands at The Big Treehouse, a campground attraction near Lake City, so visitors can compare the 271-foot original with a miniature version. The bridge is also recorded in the Historic American Engineering Record, and photographs of it are held on Wikimedia Commons.