<P> Some locks are operated (or at least supervised) by professional or volunteer lock keepers . This is particularly true on commercial waterways, or where locks are large or have complicated features that the average leisure boater may not be able to operate successfully . For instance, although the Thames above Teddington (England) is almost entirely a leisure waterway, the locks are usually staffed . Only recently have boaters been allowed limited access to the hydraulic gear to operate the locks when the keeper is not present . </P> <Ul> <Li> Powered operation . On large modern canals, especially very large ones such as ship canals, the gates and paddles are too large to be hand operated, and are operated by hydraulic or electrical equipment . On the Caledonian Canal the lock gates were operated by man - powered capstans, one connected by chains to open the gate and another to draw it closed . By 1968 these had been replaced by hydraulic power acting through steel rams . Even on smaller canals, some gates and paddles are electrically operated, particularly if the lock is regularly staffed by professional lock keepers . On the River Thames below Oxford all the locks are staffed and powered . Powered locks are usually still filled by gravity, though some very large locks use pumps to speed things up . </Li> <Li> Fish Ladders . The construction of locks (or weirs and dams) on rivers obstructs the passage of fish . Some fish such as lampreys, trout and salmon go upstream to spawn . Measures such as a fish ladder are often taken to counteract this . Navigation locks have also potential to be operated as fishways to provide increased access for a range of biota . </Li> <Li> Weigh lock . </Li> </Ul> <Li> Powered operation . On large modern canals, especially very large ones such as ship canals, the gates and paddles are too large to be hand operated, and are operated by hydraulic or electrical equipment . On the Caledonian Canal the lock gates were operated by man - powered capstans, one connected by chains to open the gate and another to draw it closed . By 1968 these had been replaced by hydraulic power acting through steel rams . Even on smaller canals, some gates and paddles are electrically operated, particularly if the lock is regularly staffed by professional lock keepers . On the River Thames below Oxford all the locks are staffed and powered . Powered locks are usually still filled by gravity, though some very large locks use pumps to speed things up . </Li> <Li> Fish Ladders . The construction of locks (or weirs and dams) on rivers obstructs the passage of fish . Some fish such as lampreys, trout and salmon go upstream to spawn . Measures such as a fish ladder are often taken to counteract this . Navigation locks have also potential to be operated as fishways to provide increased access for a range of biota . </Li>

How does a lock work on a river