Twenty environmental groups have joined forces to demand the Victorian Government conduct an independent study to inform its new waterways strategy, but the state says it can do its own science.

Environmentalists are calling for an independent look into Victoria’s rivers, wetlands and groundwater, accusing the government of breaking a pre-election promise by denying it, saying the Government's Victorian Waterways Management Strategy does not go far enough.

Groups from across the state - led by the Victorian National Parks Association and Environment Victoria - published a joint statement saying an independent study is overdue, as the last inquiry of its type was undertaken in 1991.

Environment Minister Ryan Smith says the Government has it covered: “We want to make sure that we do the work in one spot... we don't want to duplicate work - we're dealing with taxpayers' money, with public money here... I think when we came to Government it was clear to us we could get the work done through the department as part of the overall waterways strategy.”

Mr Smith has also claimed the outcomes and the terms of reference for the departmental strategy go beyond the scope of the Victorian Environmental Assessment Council.