The NSW Government has agreed to let floodwaters flow to the Murray River's parched lower lakes in South Australia. 

But just when and how much water will make it into South Australia remains to be determined after the two states reached an in-principle agreement to release reasonable environmental flows across the border.

Talks today between NSW Premier Kristina Keneally and South Australian Premier Mike Rann have resulted in excess water being used to replenish lakes Alexandrina and Albert, south of Adelaide.

Ms Keneally's instructed NSW officials attending a meeting of Murray-Darling Basin officials tomorrow to work with their South Australian counterparts.