Laos being a land-locked country surrounded by other countries with equally cheap labour but cheaper transportation to the markets, foreign investment did not focus on labour-intensive industries, but on the exploitation of its natural resources. Hydroelectricity in particular has been a popular, if somewhat controversial, source of revenue to Laos, and hydroelectric dams have been built on several tributaries of the Mekong causing severe consequences to the ecosystem as well as the displacement of entire communities into newly built resettlement areas.