Prime Ministers from Cambodia, Laos, Thailand, and Vietnam arrived in Hua Hin, Thailand for the first summit concerning the Mekong River.
The one-day summit is set to begin as the Mekong and its tributaries suffer from a severe drought that dropped the rivers to a 50-year low.
Activists and villagers living along the Mekong cast suspicion on China's hydropower dams upstream, the only dams on the river. China denies the dams have contributed to the drought and that has been supported by analysis from the Mekong River Commission, the organizer of the summit.
But delegates to the Mekong summit say China needs to share more data on how it operates its dams.
Isra Sunthornvut is an official in the Thai Prime Minister's office.
"I think there is growing speculation. That is all. Suspicion, I would suppose, that there is a direct relationship. We do not know the facts. But, we would like to know the facts."
Officials from the Mekong River countries held bilateral discussions Sunday, including with officials from Burma and China.
Little information was released from the meetings.
Jeremy Bird is head of the Mekong River Commission, which helps facilitate cooperation among river countries. He says all the attention is on China and getting more information on how it operates its upstream dams.
"We have been talking for some time and communicating about increasing data. So, this is not new. But I think the drought situation has provided a new focus and a new intensity on that."
China agreed last month to provide more information on water flows for two of four dams it has on the Mekong.
But China has also been filling the reservoir of a massive hydropower dam in the wet season so it can be released for continued power generation in the dry season.
Bird says China needs to provide information on that dam as well to prepare people living downstream for when it releases more water in the dry season.
"Although that is generally beneficial in terms of alleviating the sorts of problems we are seeing now, it also has some concerns in terms of people who are relying upon river banks for gardens, for agriculture, in the dry season. For people who are used to fishing in particular areas."
Bird says they would also like to have a procedure for emergency situations when China has to change its dam operations.
He says they would like China to notify the Mekong River Commission in advance when water flows, sediment, and water quality will be affected, so they can quickly warn people downstream.