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- Oak Avenue Hampton
- Oakhill Park Wood
- Oak Hill Wood - Barnet, London
- Oak Tree Heath
- Oakerthorpe – Derbyshire
- Oakfrith Wood
- Oakham
- Oakleigh Way
- Oakwell Park
- Oakwood and Blacklow Spinneys
- Oare Marshes
- Occombe Farm & Scadson Woods
- Ock Meadow
- Occombe Valley Woods
- Ockham and Wisley
- Ockwells Park
- Offerton Wetlands
- Ogden Water
- Old Common
- Old Denaby Wetland
- Old Lodge, Nutley
- Old Roar Gill & Coronation Wood
- Old Town Park
- One Tree Hill
- Otterhead Lakes
- Oughtonhead Common
- Owlet
- Owlet Plantation – Lincolnshire
- Owston Ferry Castle – North Lincolnshire
- Oxenbourne Down
- Oxhey Woods
- Oxleas Wood/Shooters Hill Woodlands
- Oxmoor Copse
Read more about this topic: List Of Local Nature Reserves In England