Prior to the barrages, during periods of low flow, tidal effects and the intrusion of seawater were felt up to 250 km upstream from the mouth of the River Murray, approximately as far inland as present-day Swan Reach.
From the 1900s, with the advent of large irrigation schemes, landowners along the lower reaches of the river strongly urged for the construction of barrages, primarily to keep the water fresh in the lower reaches of the River Murray, as well as Lake Albert and Lake Alexandrina.
In 1931, the Murray Darling Basin Commission authorized the construction of five barrages. Work on the barrages commenced in 1935 and was completed in 1940. South Australia's Engineering and Water Supply Department undertook the works, with costs shared equally by the Governments of South Australia, Victoria, New South Wales and the Commonwealth of Australia.
For more information refer to this article on the barrages.