The release of water is part of a new drought stimulus package announced by the Federal Government on Thursday.
The Commonwealth will help South Australia turn on a desalination plant in return for the additional flows.
The water is expected to grow up to 120 000 tonnes of fodder.
"This is a practical measure which both deals with the hardship along the Murray, but importantly, deals with making available more fodder," Prime Minister Scott Morrison said.
The package also includes $1 million for each of the 122 drought-affected councils and shires along the east coast, if they need it.
At least six new shires and councils will also be offered $1 million.
A new program will also allow small businesses dependent on agriculture to apply for loans of up to $500 000 that can be used to pay staff, buy equipment and refinance.
There will also be $10 million for schools facing hardship as a result of the ongoing drought, including fee concessions for boarding students.
Another $5 million will help assist child care centres experiencing decreased demand and the government will redirect $200 million from the Building Better Regions Fund to support drought-stricken communities, and pump an extra $138.9 million into road projects.
More to come.
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