Dagenham Brook is a minor tributary of the River Lea. It is located in the London Borough of Waltham Forest and is the traditional eastern limit of Leyton Marshes.
The brook flows from the River Lee Flood Relief Channel, close to Forest Road (near Blackhorse Road), past Walthamstow Reservoirs. It passes under Lea Bridge Road and skirts the boundary of Leyton eventually reaching a pumping station close to New Spitalfields Market.
The brook has been designated a site of Local Nature Conservation Importance. Different species of birds that can be spotted here include the kingfisher, and mammals such as fox and rabbit can also be seen.