A huge coal mine will be built next to some of the most productive farmland in NSW after receiving final approval.

The Watermark open-cut mine, on the Liverpool Plains near Gunnedah in northern NSW, will go ahead after the NSW Planning Assessment Commission determined that farming could proceed on the fertile blacksoil plains next to the mine site.

The commission also determined that groundwater impacts should be minimal and farmers should receive compensatory water from the mine operator if their supplies were harmed by the mine.

Farmers have been stridently opposed to the mine plan and raised fears about the impact it would have on water availability on the Liverpool Plains, which is a key food production area.

The Watermark mine, owned by Chinese coal giant Shenhua Group, will extract up to 10 million tonnes of coal a year for 30 years.

Environmental protection group Lock the Gate attacked the approval, saying it destroyed the credibility of NSW mining laws.

Lock the Gate national co-ordinator Phil Laird said the mine would jeopardise farmlands on the Breeza Plain and the productive Namoi Alluvial Aquifer.

By Peter Trute