The fate of a 50-year-old national park in western NSW is "at the mercy of water managers" regardless of the region's critical environmental role the reserve was set up to protect, ecologists and locals say.

The Kinchega National Park, about 100 kilometres south-east of Broken Hill, borders the Tandou irrigation property that Barnaby Joyce's federal agricultural department paid $78 million for its water rights last year.

The park, which contains half of Lake Menindee, is one of at least four sanctuaries in the NSW section of the Murray-Darling Basin where goals of the Office of Environment and Heritage's National Parks and Wildlife Service face being overridden by other demands, such as from irrigation, environmentalists said.

Lake Menindee in far west NSW in November 2016. Credit:Nick Moir

"About 28 per cent of Kinchega is wetland and [OEH] have had no control over the water," Richard Kingsford, a professor of environmental science at the University of NSW, said. "It's at the mercy of water managers."