The storage reservoir is bordered by Sewardstone and Chingford to the east and Brimsdown and Ponders End to the west, and covers 420 acres (170 hectares), making it the largest in London.

The reservoir was conceived as part of an overall plan for the Lea Valley and was laid before the Royal Commission on Water Supply (Balfour Committee) in 1893.

The external grassed embankment consists of a central puddle clay core with shoulder filling comprising a mixture of river terraced gravels and alluvial deposits.

The key engineering parameters are:[2] Located in the NW corner is the original inlet pumping station by W.B.

[5] The siphons are located in the south east corner of the reservoir and discharge is into the River Lee Diversion.

[6] It is a major wintering ground for wildfowl and wetland birds, including nationally important numbers of some species.