Stakeholders in the aquaculture industry are currently seeking the development of sustainable production systems and methodologies to measure sustainability. The present study evaluated the environmental, social and economic dimensions of sustainability of a net-cage tilapia production system with two stocking densities implemented in a reservoir in the semi-arid northeast region of Brazil during an extended drought event. The three dimensions of sustainability were evaluated through a set of 33 indicators. The Internal Rates of Return were below the Minimum Attractive Rates of Return and the Net Present Value indicator was negative for both stocking densities, showing no attractive financial benefits and no capital return capable of generating sufficient annual profits and revenues to keep the system in operation over time. The activity improved the local food supply and quality of animal protein in the state where the enterprise is carried out. Compensation of labor represented 22 and 24% of the production costs with 125 and 100 fish/m3, respectively. Various age groups and ethnic groups were represented among the employees, but the enterprise was operated only by men. Phosphorus accumulations were 2.1 and 2.0 kg/tonne and particulate material accumulations of 110 and 100 kg/tonne for 125 fish/m3 and 100 fish/m3, respectively. The prolonged drought conditions that occur in the Brazilian semiarid region can compromise the environmental, economic and social sustainability of fish farming in reservoirs in the region.