The Thames about Oxford is often called the Isis. Caesar (De Bell. Gall. v. 1 1) says that at the time of his invasion of Britain it was called Tamesis. In the first statute passed for improving the navigation of the river near Oxford (21 Jac. I.) it is called the river of Thames, and it was only in a stat ute of George II. (1751) that the word Isis appears. The flow of the Thames varies greatly, according to the season of the year. In very dry summers the flow at Teddington has been known to fall as low as 200,000,000 gal. per day and as high as 20,000, 000,000 gal. in a rainy season. Flooding of the surrounding coun try is not uncommon, and it becomes a serious menace to the low lying parts of London, where the river is tidal, when flooding coincides with high spring tides. The importance of storage reser voirs is manifest under such conditions of flow, especially bearing in mind the ever increasing needs of the London district. The water-supply of London is considered under that heading; it may be noted here that the Thames forms its chief source of supply, but apart from this the corporation of Oxford and two companies in the Staines district have powers to draw water from the river. Throughout the whole of the Thames watershed, and especially in the 3,80o sq.m. above the intakes of the water companies (at Hampton or in the vicinity), the Thames Conservancy has en forced the requirements of parliament that no sewage or other pollution shall be allowed to pass into the Thames, or any water communicating with it. The Thames is navigable for rowing-boats as far upwards as Cricklade and for barges as far as Lechlade. At Inglesham, three-quarters of a mile above Lechlade, the Thames and Severn canal has its junction with the Thames. Barges draw ing 3 ft. 6 in. can now, even in the summer season, navigate from London to Inglesham.
In 1771 an act of parliament was passed authorizing the construction of pound locks on the Thames above Maidenhead Bridge. In pursuance of the powers thus granted, the Thames Commissioners of that day caused locks to be built at various points above Maidenhead, and between 18i o and 1815 the Corporation of London carried out river works on the same lines as far down the river as Teddington. The works as subsequently maintained by the Thames Conservancy ensure an efficient head of water during the drier seasons of the year, and facilitate the escape of winter floods. The number of locks is 47, including four navigation weirs above Oxford. The uppermost
lock is St. John's, below Lechlad.; ; the lowest is Richmond.
The canals in use communicating with the Thames, are the Thames and Severn canal, the Oxford canal, the Kennet and Avon canal from Reading to the Bristol Avon, the Grand Junction at Brentford, the Regent's canal at Limehouse, the Surrey canal at Rotherhithe, the Gravesend and Rochester canal (Southern Rail way Co.). Navigation is also carried on by the Medway to Ton bridge, on the lower parts of the Darent, Cray and Wey. The Woking, Aldershot and Basingstoke canal joins the Wey, but is little used. The Wilts and Berks canal, joining the Thames at Abingdon, is disused. By means of the Grand Junction and Ox ford canals especially, constant communication is maintained between the Thames and the great industrial centres of England. The trade on the upper Thames is steady, though not extensive. The vast trade on the estuary, which lies within the bounds of the port of London, as well as the bridges over the river in the Lon don area, is considered under LONDON. The utility of the river is great in the opportunities for exercise and recreation which it affords to the public, especially to Londoners. Rowing boats, sail ing boats and motor boats ply its waters. There are fixed prices for the passage of the locks. During the season regattas take place, of which the Henley Royal Regatta is pre-eminent. The Oxford and Cambridge boat-race from Putney to Mortlake on the tideway, the summer eights and the "torpids" at Oxford Uni versity, and the school races at Eton and Radley should also be mentioned.
In 1857 the Thames Conservancy Board was established. Its powers were increased and its constitution varied in 1864, 1866 and 1894, but the creation of the Port of London Authority (see LONDON) limited its jurisdiction. Fish are abundant, especially coarse fish such as pike, perch, roach, dace and barbel. Of trout there are many fine specimens, especially at the weirs. The right of the public to take fish freely from the river has been frequently under dispute and to-day fisheries are under the regulation of by laws made by the Thames Conservancy, which apply to the riparian owners as well as to the public generally. These by-laws are carried into effect by officers of the conservators, assisted by the river-keepers of the various fishing associations. The principal associations are those at Oxford, Reading, Henley, Maidenhead and Windsor, and the Thames Angling Preservation Society, whose district is from Staines to Brentf ord.