Possible Clues:

• 'Blue --', single by Roy Orbison released in 1963
• A buoy out of place in marshy outlet
• Wet and marshy part of Louisiana
• Cajun waterway
• "The __ City": Houston nickname
• "Swamp People" setting
• Readers after a book looking up US outlet
• Spoonbill habitat
• Ecosystem susceptible to eutrophication
• Boggy biome