The upper Chagres and its seven tributaries flow into Lake Alajuela (formerly Madden Lake), the reservoir created by the Madden Dam. As these rivers contribute 45 percent of the total water for the canal, the lake is an essential part of the watershed of the canal zone. The lake has a maximum level of above sea level, and can store one third of the canal's annual water requirements for the operation of the locks. Lake Alajuela is not part of the navigational route, so there are fewer restrictions on its water level than for Gatun Lake. Water from the reservoir is also used to generate hydroelectric power and to supply Panama City's fresh water.
