[citation needed] The River Lea forms the boundary with the London Borough of Hackney, and the marshes lie within the Lee Valley Park.

The 90.7 acres (36.7 ha) area of Walthamstow Marshes south of these escaped both development and use for gravel excavation,[3] remaining a relatively untouched refuge for wildlife, crossed only by the railway lines in 1840 and 1870.

They contain a variety of plant communities typical of a former flood plain location, such as a range of neutral grassland types, sedge marsh, reed swamp, sallow scrub and areas of tall herb vegetation.

The marshes contain several species of insect with a restricted distribution in the London area such as the Essex skipper butterfly Thymelicus lineola, an uncommon Parasite fly Ligeria angusticornis, a pyralid moth Shoeribius micronellus and the sporadic breeding by the nationally endangered marsh warbler.

A variety of wintering birds visit the marshes and neighbouring reservoirs while in autumn flocks of finches are to be found feeding on the seeds of the tall herbs.