The substantial reduction in wild fish catch caused by dam developments, which has been documented in major river basins such as the Columbia and Mississippi, means a substantial loss of animal protein, a source that needs to be replaced somehow. Such a shift would have knock-on effects on land use, the economy, the environment and society. Replacement of fish protein through livestock and protein rich crops would require a significant increase in agricultural area and water use. To grow livestock or protein sources, such as soybeans requires water for irrigation of fields and pastures as well as a substantial increase in agricultural land. With the prospect of an increased food and water demand, which is already adding to the pressure on water and land, this is probably not a sustainable scenario. Most likely, the need for imported foodstuff would increase along with increased prices for protein, affecting the poor. As an example from the Lower Mekong Basin reveals proposed dam construction in the Lower Mekong Basin predicted to considerably reduce fish catch place heightened demands on the resources necessary to replace lost protein and calories. Additional land and water required to replace lost fish protein with livestock products have been modelled using land and water footprint methods. Two main scenarios cover projections of these increased demands and enable the specific impact from the main stem dam proposals to be considered in the context of basin-wide hydropower development. Scenario 1 models 11 main stem dams and estimates a 4–7% increase overall in water use for food production, with much higher estimations for countries entirely within the Basin. Land increases run to a 13–27% increase. In scenario 2, covering another 77 dams planned in the Basin by 2030 and reservoir fisheries, projections are much higher: 6–17% for water, and 19–63% for land. These are first estimates of impacts of dam development on fisheries and will be strongly mediated by cultural and economic factors (Orr et.al.2012). Such increased water requirements would probably be possible to accommodate, but a requirement for additional pasture land at the mentioned scale is presumably unrealistic considering that the agricultural land area in the Mekongbasin is constant or slightly declining. The alternative would be importing food, which would result in land use changes and affect water, energy and food security issues in exporting countries as well as placing economic pressure on the importing countries and increasing food insecurity for poor people due to a need to buy protein sources. This would add to regional, and perhaps even global, food insecurity.