Frog symphony and ancient trees in a verdant Louisiana swamp

This June 3, 2018 photo shows a walkway in the Barataria Preserve, part of Jean Lafitte National Historical Park and Preserve in Marrero, Louisiana, just outside of New Orleans. Visitors will find a symphony of frogs, the fan-shaped fronds of palmettos and strange formations of cypress trees known as knees pushing up through the swamps amid the preserve's woods and wetlands. (AP Photo/Beth J. Harpaz)
Moss cascades from tree branches overhead in this June 3, 2018 image of the Barataria Preserve, part of Jean Lafitte National Historical Park and Preserve in Marrero, Louisiana, just outside of New Orleans. Visitors will also find a symphony of frogs, fan-shaped palmettos and strange formations of cypress trees known as knees pushing up through the swamps amid the verdant preserve's woods and wetlands. (AP Photo/Beth J. Harpaz)

This June 3, 2018 photo shows visitors taking in the verdant landscape of woods and wetlands at the Barataria Preserve, part of Jean Lafitte National Historical Park and Preserve in Marrero, Louisiana, just outside of New Orleans. The park offers a symphony of frogs, fan-shaped palmettos and strange formations of cypress trees known as knees pushing up through the swamps. (AP Photo/Beth J. Harpaz)

This June 3, 2018 photo shows a verdant landscape in the Barataria Preserve, part of Jean Lafitte National Historical Park and Preserve in Marrero, Louisiana, just outside of New Orleans. Visitors will find a symphony of frogs and strange formations of cypress trees known as knees pushing up through the swamps amid the preserve’s woods and wetlands. (AP Photo/Beth J. Harpaz)

MARRERO, La. — It was 93 degrees and humid when I set out on a 4-mile stroll through a Louisiana swamp.