Song Dong Nai (song means river) or Donnai, is 300 miles (480 km) long, rising as the Da Dung in the mountains of south central Vietnam.

        The Cat Loc region in the north principally consists of high steep mountains (altitude 200-600 meters), which make up the southern end of Vietnams central plateau. These mountains are generally flat-topped and are the source of springs and streams feeding the Dong Nai River.

        The annual monsoons, and associated flooding events are integral to the region's hydrological system. The Dong Nai River is the second largest river system in south Vietnam: with an average channel width of around 100m. The largest is the Mekong.

        The Dong Nai flows south-west past Bien Hoa and joins with the Saigon River below Saigon to form an extensive delta on the South China Sea. There are rapids and waterfalls on its upper reaches.

        The Dong Nai Basin is the third largest basin in Viet Nam with a catchment area of about 40,000 km. The primal importance of the basin derives from the fact that it contained the biggest city and commercial center in Viet Nam – Saigon (now Ho Chi Minh City).