After the dam project was shelved, the proposal to UNESCO was written by Seub Nakhasathien and another outspoken opponent of the Nam Choan Dam, and, in December 1991, Thung Yai Naresuan together with the adjoining Huai Kha Khaeng Wildlife Sanctuary was declared a Natural World Heritage Site by UNESCO. In the nomination, the "outstanding universal value" of the two sanctuaries is, in first place, justified with their extraordinary high biodiversity due to their unique position at the junction of four biogeographic zones, as well as with its size and "the undisturbed nature of its habitats". The death of Seub Nakhasathien, the forest conservator instrumental in the UNESCO listing who committed suicide in 1990, transformed the status of Thung Yai Naresuan and the adjacent Huay Kha Kaeng Complex into a sacrosanct site and inspired many young persons to become forest patrol staff.