A senior US diplomat on Thursday said China’s “manipulation” of water flows in the Mekong River – currently at record lows – was an immediate challenge to the Association of Southeast Asian Nations , signalling the issue could be on the agenda in a regional forum next week. The comments by David Stilwell, the assistant secretary of state for East Asia and the Pacific, are the latest evidence that the 4,350km river, on which 60 million Southeast Asians depend, has become a new front in the US-China rivalry. The next US-China battleground: Chinese dams on the Mekong River? Amid heightened scrutiny of the issue, Chinese Premier Li Keqiang in late August told a China-led forum that included five downstream Southeast Asian countries that Beijing would begin sharing year-round hydrological data of the river, known as the Lancang on the mainland. Stilwell, speaking in a webinar co-organised by the United States Institute of Peace and Singapore’s Lee Kuan Yew School of Public Policy, said the water flow issue was among the “troubling trends” in the Mekong region. “One especially urgent challenge is [China’s] manipulation of the Mekong River flows for its own profit at great cost to downstream nations,” Stilwell said. He cited a recent report that “documented [that China] has been manipulating the water flows along the Mekong for 25 years, with the greatest disruption in natural flows coinciding with major dam construction and operation”. While Stilwell did not name the report, Beijing and Washington have in recent months been sparring over rival studies on the state of the river’s flow in the five downstream Southeast Asian nations: Laos, Myanmar, Thailand , Cambodia and Vietnam. Why Asean should treat the Mekong like the South China Sea The US-based Eyes on Earth in April concluded that Chinese dams had been holding back 47 billion cubic metres of water. That report was commissioned by the United Nations-backed Sustainable Infrastructure Partnership and the Lower Mekong Initiative – a group comprising the five Southeast Asian nations downstream of the river as well as the United States . A rival study, a collaboration between Tsinghua University and China’s Institute of Water Resources, argued the contrary, saying the Chinese dams alleviated the Mekong area’s drought problems. It said the dams enabled release of stored water from the wet season in times of low flows. Flows in the river are at record lows for a second consecutive year. Stilwell said the crisis was “devastating harvests [and] threatening food and water security throughout the region”. He said: “These things have great potential for greater instability. The US is working with Mekong countries, the Mekong River Commission and international partners to ensure calls for water data transparency from [China] are answered.” The diplomat, who along with Secretary of State Michael Pompeo has been fleshing out Washington’s toughened China policy in various public forums in recent months, also offered his views on the Association of Southeast Asian Nations ( Asean ). Foreign ministers of the 10-nation grouping as well as counterparts from global partners such as Pompeo, China’s Wang Yi, Russia’s Sergey Lavrov and India’s S. Jaishankar will next week participate in a series of virtual meetings that include the annual Asean Regional Forum (ARF). These meetings were pushed back from early August by hosts Vietnam – the Asean chair for the year – in the hope that in-person meetings could take place. But they will now go ahead virtually. The ARF is the third most important event in the annual Asean calendar, after the twice-yearly leaders’ summits. In a statement on Wednesday, the US State Department said alongside the scheduled Asean-linked meetings, Pompeo would co-chair an inaugural Mekong-US Partnership Ministerial Meeting with the five downstream countries. Stilwell said he hoped Asean countries – some of which are in a dispute with China over the South China Sea – would continue to use a “strong collective voice” to advance their interests. Asked during a brief question and answer session about the perception within Asean that member states were increasingly being forced to choose a side in the US-China rivalry, Stilwell said he did not understand why such a narrative persisted. “I don’t remember in any of my interactions ever laying out a choice,” said the diplomat, a former US air force Brigadier General who assumed his current position in June last year. Japan’s Motegi pledges aid to Mekong countries “The choice is for sovereignty, the choice is for these countries to do what in [Asean’s] pluralistic framework best benefits themselves, their people and their international interests,” he said. He made thinly veiled jabs at China, suggesting Beijing threw its weight around with its less-powerful neighbours instead of dealing with them as equal partners. “There’s a choice there, and the choice is to support those rules and norms and continue them, or go with another approach that looks a lot more like might makes right,” Stilwell said. He told the moderator, the Singapore-based former US defence department official Drew Thompson, that he hoped to get the line of thought that Asean countries were under pressure to align with either superpower “shuffled to the side”. Instead, he said he hoped to “make a more reasonable presentation of what those choices are”.