A local Liberal MP has launched an extraordinary attack on his Nation Party  coalition colleagues over their renewed interest in a new dam on the Shoalhaven River, warning of war, if the proposal goes past first base.

Proposals for the Welcome Reef Dam  at O'Allen Ford near Nerriga surfaced again at the National Party state conference in Bowral, over the weekend.

A dam on the upper reaches of the river was first proposed more than 100 years ago, and was placed on an indefinite hold in 2000.

Kiama Liberal MP Gareth Ward says a dam at Welcome Reef is not acceptable in any shape or form and unless the Nationals abandon the idea,  there will be trouble in coalition ranks