While three-quarters of the residents of Amazonia live in Brazil, the population has been growing in the Amazonian region of all the countries that share the basin. Population density in Amazonia has increased in the past two decades, from 3.4 inhabitants per square kilometer in the 1990s to 4.2 in the first half of the 2000s. Population density is lowest in Venezuela (0.38 people per sq km) and Bolivia (1.1 per sq km), and highest in Peru (5.57), Ecuador (5.44) and Brazil (4.96). Many Amazonian cities grow with little or no planning and with a shortage of basic services, such as water, sewage and waste disposal.
Population growth in Amazonia is driven largely by extractive industries. People migrate to the region for jobs in the petroleum industry in Ecuador and to the alluvial gold mining camps in Peru. With international gold prices high, a gold rush has made Madre de Dios the Peruvian region with the fastest-growing population.
Construction of infrastructure, such as hydroelectric dams and highways, also lures workers to the region. While some move on, many stay once the construction work is done. Critics of major infrastructure projects, such as the Regional Infrastructure Integration Initiative for South America (IIRSA, for its Spanish initials), say too little money is invested in measures to mitigate the indirect impacts of such projects, such as those stemming from increased migration to the region. A recent study found more than 50 infrastructure projects planned for Peru alone, with no overall vision or plan for development in the Peruvian Amazon and no consideration of the combined impact of highways, dams, canal systems, and petroleum development on the region.