Ma
- Macatawa River - Michigan
- Machias River - Eastern Maine
- Machias River (Aroostook River) - Northern Maine
- Mackinaw River - Illinois
- Macoupin Creek - Illinois
- Mad River - California
- Mad River - Maine
- Mad River - Eastern New Hampshire
- Mad River - Central New Hampshire
- Mad River - Ohio
- Mad River - Vermont
- Mad River - Washington
- Madison River - Wyoming, Montana
- Magalloway River - Maine, New Hampshire
- Magothy River - Maryland
- Mahoning River - Ohio, Pennsylvania
- Maidford River - Rhode Island
- Maiford River - Rhode Island
- Malad River - Idaho
- Malad River - Utah and Idaho
- Malden River - Massachusetts
- Malheur River - Oregon
- Manasquan River - New Jersey
- Manatee River - Florida
- Manhan River - Massachusetts
- Manistee River - Michigan
- Manistique River - Michigan
- Manitowish River - Wisconsin
- Manitowoc River - Wisconsin
- Manumuskin River - New Jersey
- Mapes Creek - Washington
- Maple River - Iowa
- Maple River - Minnesota
- Maple River - North Dakota
- Maquoketa River - Iowa
- Marais des Cygnes River - Kansas, Missouri
- Marengo River - Wisconsin
- Marias River - Montana
- Marion River - New York
- Marmaton River - Kansas, Missouri
- Martin River - Alaska
- Marys River - Illinois
- Marys River - Oregon
- Mascoma River - New Hampshire
- Mashpee River - Massachusetts
- Maskerchugg River - Rhode Island
- Mat River - Virginia
- Matanuska River - Alaska
- Matanzas River - Florida
- Matfield River - Massachusetts
- Matta River - Virginia
- Mattapoisett River - Massachusetts
- Mattaponi River - Virginia
- Mattatuxet River - Rhode Island
- Mattole River - California
- Maumee River - Indiana, Ohio
- Maunesha River - Wisconsin
- Maurice River - New Jersey
- Maury River - Virginia
- Mayo River - Virginia, North Carolina
- Mazon River - Illinois
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