Premier Jay Weatherill says he’ll write to all Federal Opposition and Greens MP’s urging unity and calling on them to support the 3200 gigalitres of annual flows for the Murray.

The Julie Gillard proposal announced in the Lower Lakes last week is an increase of 450 gigalitres on the previously-recommended volume of water suggested for the Murray-Darling Basin plan.

Mr Weatherill says backing from SA Liberals would ensure the plan proceeds.

Mr Weatherill has warned also his threatened River Murray High Court challenge remains "on the table" if a detailed plan to rescue the system does not deliver long-term health.