Medway Estuary and Marshes is a 4,748.8-hectare (11,735-acre) biological Site of Special Scientific Interest which stretches along the banks of the River Medway between Gillingham and Sheerness in Kent.

[1][2] It is a Nature Conservation Review site, Grade I,[3] a Ramsar internationally important wetland site,[4] and a Special Protection Area under the European Union Directive on the Conservation of Wild Birds.

[5] Part of the land area designated as Medway Estuary and Marshes SSSI is owned by the Church Commissioners[6].

This site is internationally important for its wintering birds, and nationally important for its breeding birds.

It is also has an outstanding flora, such as the nationally rare oak-leaved goosefoot and the nationally scarce slender hare's-ear.