The environmental assessment report prepared by the Hunter Water Corporation as part of its application for planning approval of the dam has been slammed by senior officials in the NSW Office of Water and the Hunter-Central Rivers Catchment Management Authority.

A letter to the Department of Planning signed by the general manager of the management authority, Fiona Marshall, says two key justifications for the dam - the impact of climate change and the increased demand for water supplies due to population growth - are based on misleading or outdated data.

A second document, also uncovered in a call for papers by the upper house, shows a senior manager from the NSW Office of Water believes the project ''will not meet the objectives and principles of the state's water legislation and policy''.

The letter to the Department of Planning, signed by Mark Mignanelli, the manager of major projects and assessments, says endangered flora would be destroyed by the dam in a way that is not consistent with government policy.

Furthermore, the ''significant adverse effects'' of the dam on wetlands, the flow of water in the Williams River and vegetation will be long term and cannot be mitigated, it says.

The documents are the latest in a string of damning assessments by various government agencies of the proposed dam, which was announced a week after a local Labor MP, the former Aboriginal affairs minister Milton Orkopoulos, was charged with child sex offences.

The Labor Government has consistently argued that the concerns are minority views within the bureaucracy or that documents were draft or unsigned. A spokesman for Hunter Water Corporation said these reviews were some of ''a wide range of views and opinions about this major infrastructure project''.

The NSW Greens called for the dam to be dumped.