Bayou Sauvage National Wildlife Refuge, located 15 miles east of New Orleans, is a great spot for a flat, scenic run. The Refuge is a protected marshland, popular with birders. You will see alligators! The route starts at the parking lot off Highway 90, near the Madere Marsh Boardwalk. Begin with a short loop on a boardwalk through wetlands, and then follow the Levee trail, which is a flat, gravel trail along a canal, for ~3 miles to near I-10. You will see alligators!
Many thanks to Aurélie Vilmer, who suggested this route!