Human development not only carries monetary impacts on goal markets, it also generates effects on other markets, new interactions between societies (e.g. relocation of population, change in the growth ratio, etc.), and degradation of the environment around the impacted zone (living species, water, soil, etc.). The correct way to address a development project shouldn’t be to choose between economic development, social wellness or environmental quality; there must be equilibrium between these three components. The Gallito Ciego reservoir (Peru) was built to allow a better storage and regulation of the Jequetepeque River’s water, increasing and improving the agricultural area at the Jequetepeque and Zaña valleys. This study’s analysis was done in 2 scenarios: ex-ante and ex-post. A cost-benefit analysis for the most important crop at the zone (rice) from 1992 to 2007 was made; also a matrix of relevant indicators was built in order to observe the variation of the values during the implementation of the project. The main conclusion is that even though there is a significant positive monetary return, other indicators; like salinity of the soils, dam capacity, and growth rate; were not as good as they were expected.