Officially known as Lock and Weir No. 1.Blanchetown's lock was named for William R. Randell, the Murray's pioneer captain, who first navigated the river in 1853.
It is the River Murray's longest weir at 168.85 metres and includes a navigable pass and a sluice section, both of which can be opened during floods to maintain water flows. The associated lock allows boats to move from one level of the river to another.
The foundation stone was laid on 5 June 1915, but because of floods, it was December 1919 before the lock valves were opened. The lock was officially opened to river traffic on 5 April 1922. Some 60,000 tones of stone had been used in its construction.