The Mekong River is the 12th longest river in the world, around 4500 km, and until recently has been remarkable among its class of rivers for not being "developed." Though intensely used by people who live near, on, and in the Mekong, and though several substantial irrigation projects historically have structured portions of the Mekong Basin and the Mekong Delta, until recently the Mekong has been free of major hydroelectric dams and regional irrigation projects. Just how this relatively undeveloped but highly used river has been imagined by observers can be summarized by what cultural studies specialists call an "imaginary" - a complex of perceptions and expressions that collectively represent, in this case, a geographical phenomenon. The 1978 American film Apocalypse Now, about the Vietnam War, provided an enormously influential depiction of a long stretch of the Mekong - by way of its fictional stand-in, the Nung River, on which most of the action in the film took place. This film was deeply influenced in turn by the classic novella Heart of Darkness by the Polish-English writer Joseph Conrad - what Edward Said has decisively explained as an important anti-imperialist imperialist work of literature. In the 1990s and the first decade of this century, several dam-building projects, planned and now being constructed, have begun to domesticate the river for high-level exploitation. These projects and the responses to them have also encouraged a regional understanding of the Mekong, on a larger scale and as a basin and region rather than as a single thread of access into a place of unmitigated darkness. Paradoxically, hydroelectric dam projects and visions for regional exploitation of the Mekong - and struggles over who gets a say and how to manage that exploitation - have also encouraged regional approaches to managing fisheries, riverine environmental, and conservation efforts. This chapter discusses these collective imaginings with the purpose of encouraging a more reflective understanding of a geography that is often taken for granted in efforts to manage the Mekong.