The source of the River Thames is in a field near Kemble, Gloucestershire. The river runs about 215 miles (346 kilometres) through Gloucestershire, Wiltshire, Oxfordshire, Berkshire, Surrey, London, Essex and Kent before reaching the North Sea.

The Thames and its tributaries are part of the wider Thames river basin or 'catchment area'. All the rain falling within this area flows into the Thames, its tributaries or into underground aquifers. For more information on the hydrological cycle, see the European Environment Agency website.

Map of the Thames River Basin District

River Thames and Thames basin district map

Contains Environment Agency information © Environment Agency and database right. Reproduced by kind permission of the Environment Agency.

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1894 Map of the Thames River Basin

Map of River Basin

'Map of the Catchment Basins of the River Thames & Tributaries' (Thames Conservancy: Feb 1894).

© Reproduced with kind permission from the Surrey History Centre (Ref: QS6/8/Add6)

Click on map to see larger version [PDF] 

This map was produced by the Thames Conservancy, probably to go with the Thames Conservancy Act of 1894. This Act extended the pollution control and conservancy powers of the Thames Conservancy within the Thames catchment area (above London, with some additional powers below London).

The dotted line indicates the 'Thames Watershed', i.e. the hydrological boundaries of the Thames river basin (or 'catchment area'). You can see Thames basin boundaries with the basins of the Severn and Avon in the west, and with those of the Crouch and Medway in the east. The table on the lower right corner lists the tributaries along both banks. The total catchment area for the Thames is given as 5,334.3 square miles in this map.

Under the Port of London Act 1908, the Thames Conservancy's powers over the tidal Thames were transferred to the newly established Port of London Authority. The Thames Conservancy retained conservancy and navigation powers for the non-tidal river and the catchment area above London until 1974. Following the 1973 Water Act, the Thames Water Authority absorbed the Thames Conservancy and took on conservancy responsibilities for the whole Thames river basin.