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| Macey Cove (4) | machine learning (1) | Mack Arch (1) |
| Mack Landing (3) | Mackenzie River (1) | Mad River Slough (1) |
| Magelona sacculata (1) | Magma (118) | magnesium (3) |
| Magnetism (31) | Maideu Lake (1) | Maidu Lake (1) |
| Main channel (32) | Maine (2) | Makah Bay (Wa.) (1) |
| Makah Formation (1) | Malbaie River (Quebec) (1) | Malheur River (2) |
| Mallard duck = Anas plalyrhynchos (3) | Malmiana species (1) | Maltby Dairy Farm (1) |
| mammals (6) | management plans (6) | manganese (24) |
| Mangroves (1) | Manila clam = Venerupis japonica (50) | Manila clam = Venerupis japonica, Softshell clam = Mya arenaria, Bay shrimp = Crangon franciscorum, Dungeness crab = Metacarcinus magister (Cancer magister), Green sturgeon = Acipenser medirostris, White sturgeon = Acipenser transmontanus, Shad = Alosa (1) |
| Manila clam=Venerupis japonica (1) | Manila littleneck clam = Venerupis phillipinarum (1) | Maniobra formation (1) |
| Mantle (70) | Manzanita (1) | Manzanita (Or.) (5) |
| Manzanita Beach (1) | map (162) | Maple Creek (1) |
| Maples Riffle (1) | Mapleton (Or.) (1) | mapping (1) |
| maps (75) | marbled godwit=Limosa fedoa (1) | Marbled murrelet = Brachyramphus marmoratus (11) |
| marbled murrelet=Brachyramphus marmoratus (4) | Maria Creek (1) | marinas (10) |
| marine algae (1) | marine ecology (1) | Marine Gardens (1) |
| marine habitat (1) | marine mammals (38) | marine plankton (1) |
| marine plants (7) | marine reserves (2) | Marine Science Center Dock (43) |
| Maritime transportation (3) | Marks Creek (2) | Marlowe Creek (1) |
| Marsh Creek (2) | Marsh jaumea = Jaumea carnosa (2) | marsh restoration (17) |
| marshes (37) | Marshfield (Or.) (5) | Marsters Creek (1) |
| Martin Creek (3) | Martinez formation (1) | Mary's River (1) |
| Maryland (3) | Marys River (1) | Mary’s River (1) |
| Mass movement (12) | Massachusetts (2) | Massive starlet coral = Siderastrea sidereal (1) |
| Masu salmon = Oncorhynchus masou (1) | mathematical modeling (95) | mathematics (1) |
| Matson Creek (1) | Matson Creek (Coos) (1) | Maverick Creek (1) |
| May Creek (1) | McCafferey Slough (1) | McCaffery Slough (15) |
| McCaffrey Island (1) | McClean Point (1) | McComas Creek (2) |
| McFall Creek (2) | McGee Creek (1) | McGinnis Creek (1) |
| McIntosh Formation (3) | McIntosh Slough (2) | McKay Creek (1) |
| McKenzie River (7) | McKenzie River Basin (2) | McKinley Marina (1) |
| McKinney Slough (5) | McKinney's Slough (1) | McKinneys Slough (1) |
| McLean Point (37) | McMinnville (Or.) (2) | McNabb Creek (1) |
| McSherry Creek (1) | Meadow barley = Hordeum brachyantherum (2) | Meadow Creek (5) |
| Measurements (1) | Medicine Creek (2) | Medicine Rock (1) |
| Mediomastus californiensis (1) | Mediterranean mussel = Mytilus galloprovincialis (2) | Meg's Keep (1) |
| Mehi Creek (1) | Melange (6) | Melanges (6) |
| Melco Landing (2) | Melita species (2) | Mellow Moon Creek (2) |
| Melosira species (1) | Melton creek (1) | mercury (25) |
| meroplankton (1) | Merrimack River (Mass.) (1) | Mesozoic (106) |
| metabolism (1) | Metacarcinus magister (Cancer magister) (1) | Metals (51) |
| Metamorphic (4) | Metamorphic rocks (61) | Metamorphism (10) |
| Metchosin Formation (2) | Meteorite (2) | methane (9) |
| methodology (83) | Methow River (1) | methylmercury (1) |
| Metriocnemus yaquina (1) | Mew gull = Larus canus (3) | mew gull=Larus canus (4) |
| Mexico (16) | Miami River (63) | Michigan (2) |
| Microbes (3) | microbiology (3) | Microbiome (1) |
| microfossils (1) | Midbay (1) | Middle Creek (3) |
| Middle Creek (Coquille) (1) | Middle Fork Coquille River (2) | Middle Fork John Day River Basin (1) |
| Middle Fork South Deer Creek (1) | Middle Fork Willamette River (1) | Middle Jetty (1) |
| Middle North Umpqua River (2) | Middle South Umpqua River (2) | Middle Umpqua River (13) |
| migration (15) | Military training Oregon (1) | Mill Creek (69) |
| Mill Creek (Siletz) (15) | Mill Creek (Umpqua) (1) | Mill Creek (Yamhill) (1) |
| Mill Creek (Yaquina) (5) | Mill Creek Reservoir (Yaquina River) (1) | Mill Four. dikes (1) |
| Mill's Rapid (1) | Miller Creek (5) | Miller Creek (Umpqua) (5) |
| Millicoma dace = Rhinicthys cataractae ssp. (1) | Millicoma Rive (1) | Millicoma River (25) |
| Millport Slough (22) | Millport Slough (Siletz) (2) | Millport Slough Bridge (2) |
| Millport Slough marshes (1) | Milo (1) | Minard (1) |
| Miner Creek (4) | Mineralization (7) | minerals (281) |
| mining (88) | Minnesota (2) | Miocene (178) |
| Misery Creek (2) | Mississippi (2) | Missouri Bend (1) |
| Mitchell Creek (2) | Mitchell Formation (1) | Mitchell Marsh (4) |
| mitigation (21) | Mitten crab = Eriocheir sinensis (1) | Molalla River (2) |
| Mole crab = Emerita analoga (1) | molecular biology (2) | mollusca (3) |
| Molluscan Broodstock Program (3) | molluscs (423) | molluscs, (1) |
| mollusks (60) | Monochrysis species (11) | Montana (12) |
| Monterey Formation (3) | Montgomery Creek (5) | Montgomery Creek Formation (1) |
| Moolach Beach (3) | Moolach Shores (2) | Moolack Beach (2) |
| Moon Creek (2) | Moon Creek (Nestucca River) (1) | Moonshine County Park (4) |
| Moonshine Park (2) | Moore Creek (20) | moose = Alces alces (1) |
| Moraine (1) | Morgan Creek (2) | Morgan Landing (1) |
| morphology (14) | Morrison Formation (1) | Morro Bay (1) |
| mortality (3) | Morton Creek (1) | Mosetown Creek (Smith River) (1) |
| Moss Creek (2) | Moss Creek (Kilchis) (2) | motility (1) |
| Mott Bridge (1) | Mount Mazama (1) | Mount Rainier (7) |
| Mount St. Helens (14) | Mountain rush = Juncus arcticus littoralis (1) | Mowry Landing (1) |
| Mt. Hood National Forest (1) | Mud blister worm = Polydora spp. (1) | Mud shrimp = Upogebia pugettensis (42) |
| mud shrimp=Upogebia pugettensis (1) | Muddy Creek (1) | mudflats (2) |
| Mult Creek (1) | Muns Creek (1) | Munsel Lake (Siuslaw) (2) |
| Murphy Creek (1) | Mushan Formation (1) | mussels (5) |
| Myers Creek (4) | Myers Creek Beach (1) | Myosotella myosotis (1) |
| Myrtle Creek (24) | Myrtle Creek/Tri City (1) | Myrtle formation (1) |
| Myrtle Point (2) | mysids (3) | Mytilicola orientalis (1) |
| Myxobolus insidiosus (1) | Myxobolus squamae (2) | |
