Officials said the river level is dropping faster than in recent years due to the construction of dams in neighbouring Laos and low rainfall in catchment areas.
Water levels in three main tributaries - the Nam Kam, Nam Songkhram and Nam Un rivers - is now at 10%-20% of their capacities, causing shortages of water for agriculture.
Underground water is also running dry.
Therefore, irrigation officials have stopped releasing water from Nong Han lake in Sakon Nakhon province into the Mekong river via the Nam Kam stream, to keep enough water to irrigate about 60,000 rai of farmland during the dry season.
Farmers have been told to grow crops outside irrigated zones and look for new sources of water to cope with the drought.