Sombath Somphone's wife says his family still wants to know why he disappeared.
Authorities are concerned about unease over three Hmong prisoners believed to be in poor health.
The WWF warns the Don Sahong could kill off the last dolphins on the river.
The disappearance of a civil society leader has brought the Southeast Asian national under sharper focus by rights groups.
Farmers grow less of the grain due to poor irrigation systems and the promise of better cash crop prices.