The Aldenham Country Park is a large and pleasant area easily reached if you are travelling north out of London. It is worth visiting if you want a quick breath of fresh air and a reasonably attractive place for a brief picnic. The most important point of the park is Aldenham Reservoir. It was built in 1796 to 1 _____ water level in the river affected by the newly constructed Grand Union Canal, and more recently has been used as a reserve public water supply.