The Albanese government has pledged $300 million to support regional communities that will be affected by a decision to send an extra 450 gigalitres of water down the Murray River over the next three years to ensure its environmental health.

With the bulk of that water to be achieved by buying back licences from irrigators, Environment Minister Tanya Plibersek will on Tuesday also release an expert report which she says shows the effect of buybacks on agricultural production will be far less than that caused by low rainfall or drought.