Farmers are facing massive cuts between 27 and 37 per cent to the amount of water they can take from the Murray-Darling under plans to save the river.

The Herald has learnt that the independent Murray-Darling Basin Authority will propose the cuts tomorrow when it releases key details of a new plan it has been preparing for the past 18 months.

The proposed reductions to water entitlements would ensure an extra 3000 to 4000 billion litres of water would be returned to the river's environment.

But the size of the cuts has shocked and angered farming groups, with the National Farmers' Federation saying they would ''devastate'' rural communities.

The proposed cuts will be the centrepiece of a ''guide'' to the basin plan to be released tomorrow. The document will be followed by a round of public consultation, including meetings throughout regional Australia.