sentences:  It was also used by the Heygates flour mill, and Bushell's built boats on its banks.Despite several attempts to rectify leakage, including one of the earliest uses of asphalt for this purpose, no satisfactory solution was found, and most of the canal ceased to be used for navigation in 1904.Water levels in the upper section were lowered, and a pipeline was constructed along part of the bed, so that water could still be supplied to Tring summit.