Upper Colne Marshes is a 114.1-hectare (282-acre) biological Site of Special Scientific Interest south and west of Wivenhoe in Essex.

It has an important assemblage of nationally scarce plants and diverse ditch types.

The grassland is species rich, with rare types such as sea barley, and salt marsh has the nationally uncommon lax-flowered sea-lavender.

Insects include the nationally scarce Roesel's bush-cricket.

[1] The site is in five areas, some of which are crossed by roads and footpaths.