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In the wintering population of Eastern United States , however , they are often associated with steep river valleys , reservoirs , and marshes in inland areas as well as estuarine marshlands , barrier islands , managed wetlands , sounds , and mouths of major river systems in coastal areas .
 Eastern United States
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Eastern United States