Two environmental re-engineering projects clashed in south-eastern Puerto Rico in the early twentieth century. Between 1910 and 1914 the Puerto Rican Irrigation Service built three large dams to water canefields owned by US sugar companies. The new canals and holding ponds created ideal breeding grounds for malaria-carrying mosquitoes, and demand for fieldworkers encouraged greater numbers of Puerto Ricans to work and live near these mosquito swarms. Malaria rates soared as a result. Meanwhile, public health officials tried to control malaria, but their efforts faltered, especially when efficient irrigation was prioritised above all else. It was not until the 1940s and 1950s that health officials controlled and then eliminated malaria. In Puerto Rico, malaria rose with the commitment to irrigated canefields and remained tenacious until wartime exigencies inspired greater control efforts, DDT became available and, most importantly, manufacturing eclipsed sugar production as the island's dominant economic activity.
