The larger of the two reservoirs , it holds a maximum of 9.9 billion gallons ( 37 million m ) .
The Portland Water Bureau built Dam 1 , a concrete arch - gravity dam , in 1929 to create Reservoir 1 , also known as Ben Morrow Lake .
The larger of the two reservoirs , Portland Water Bureau holds a maximum of 9.9 billion gallons ( 37 million m ) .
The Portland Water Bureau built Dam 1 , a concrete arch - gravity dam , in 1929 to create Reservoir 1 , also known as Ben Morrow Lake .