THE MEKONG: Turbulent Past, Uncertain Future, by Milton Osborne. Atlantic Monthly Press, New York, 2000, $24.

This elegiac tribute to the Mekong River is an occasion for a comfortable chair and a languorous afternoon. The intrepid armchair traveler is transported to this magnificent locale and can almost see the morning mists hanging over the banks of the river, experience that frisson of skirting whirlpools and enjoy the sunsets lingering over an aperitif.

Milton Osborne mines the written record for many interesting stories about life on and along the Mekong, dwelling longest on colonial-era explorations.

It is surprising to learn that it was not until 1994 that the exact location of the Mekong's source was traced to Tibet. It is also fascinating to read about how the swollen river backs up in the rainy season, reversing course and flooding Cambodia's great lake, the Tonle Sap. This natural phenomenon stocks the lake with a bountiful fish harvest, providing an estimated 60 percent of the protein intake of Cambodia's population. Moreover, the Cambodian rice harvest also benefits from this natural process of irrigation and fertilization, helping to explain how the great civilization of Angkor was able to sustain itself.