Check out the LakesNeedWater Blog for newspaper articles from the 1930's.
Read oral history interviews of what life was like before the barrages.
Sources:
A Timeline of River Murray history from 1802-2004 is available at the State Library of South Australia.
From the book "For They Were Fishers" a history of the South Australian Fishing Industry by Evelyn Wallace-Carter . With excerpts from her book about the Lakes and the Coorong.
Alexandrina Library Oral History transcripts
Interview with Jim Marsh Goolwa Barrage superintendent
Interview with Bert Lundstrom
Interview with Syd Smith
Interview with W.A. Pretty
Interview with Richard Spencer
Interview with Harold Bedford
Excerpts from the above interviews here.
Photos of the building of the Barrages in 1930-40
Link to the whole album http://images.slsa.sa.gov.au/mpcimg/59500/B59473.htm
Photos of mulloway pre 1950's
http://images.slsa.sa.gov.au/d/7893/D7893_8T.htm
Fisherman holding a 91 lb Mulloway at Milang
http://images.slsa.sa.gov.au/godson/2/01250/PRG1258_2_1109.htm
circa 1938
http://images.slsa.sa.gov.au/searcy/21/PRG280_1_21_128.htm
http://images.slsa.sa.gov.au/searcy/21/PRG280_1_21_131.htm
http://images.slsa.sa.gov.au/mpcimg/55250/B55176.htm
You can also search the National Archive of Australia through 'Trove'