 In 1924 a small <unk> dam was built 6 kilometres ( 4 mi ) downstream from the present Canning Dam . It was only intended as a quick fix to the water supply problem and it soon became apparent that a major reservoir was needed , although it would be nine years before work on the current Canning Dam would begin . The new dam was completed in 1940 at a cost of AU £ 1 @.@ 1 million . Engineer Russell Dumas designed the dam and directed most of its construction . 
