 All rivers discharging into the Thames and Medway and their estuaries.This section includes the coast of Kent west of Foreness Point at the northeast corner of Kent and the south coast of Essex, west of Shoeburyness.But see also 
Medway catchment

Thames catchment

All rivers discharging into the North Sea along the coast of East Anglia, including the counties of Essex (north and east of Shoeburyness), Suffolk and Norfolk as far as King's Lynn.