This paper measures the ensuing changes in productivity in the French pig sector following the introduction of the European regulation addressing water pollution by nitrates from agriculture. Productivity is measured using the Malmquist–Luenberger index. The sources of changes in productivity observed are examined by breaking down this index into its technical progress and efficiency components. The results show that in the early stages, increases in productivity were stimulated by increased efficiency, before being driven by technical progress. The estimations regarding the sources of efficiency gains for the farms in the sample (technical efficiency, efficiency of scale and environmental efficiency) are then used to estimate the indirect costs and benefits (or negative costs) linked to the introduction of the environmental regulation controlling the disposal of organic manure and the management of nitrogen surplus from pig farms. The existence of a “win-win” effect as regards the Porter hypothesis relation between efficiency and environmental regulation is highlighted for the French pig sector.