To improve the quality of water resources in France, water managers are called upon to put in place agri-environmental action plans (AEAP) at various nested spatial and temporal scales. The aim of this is to encourage farmers to change some of their practices, particularly those which lead to high levels of diffuse pollution (nitrate and pesticides). Therefore, local decision makers are constantly on the lookout for decision tools to help them assess the potential impact of agro-environmental measures, as well as applying them in the best, most effective way. By participating in the development of a "Grenelle" water abstraction action plan in SW France, we were able to develop an innovative computerized management and decision support tool. The proposed "SIGPA" (Information System for Action Plan Governance) model displays the overall approach to helping public decision making within pesticide action programs. It can be applied in various contexts, using local models or specific indicators and addressing the needs of water managers. The proposed conceptual models and associated information system provide the support to enable stakeholders and decision makers to identify the most effective and least expensive actions for limiting pesticide and nitrate pollution. The system organizes and structures information obtained from local stakeholder networks. A prototype of the spatial data warehouse was used, based on data collected as part of a "Grenelle" action plan in a wide area (3600 km2) within the Charente river basin. Using a number of spatial data warehouses, it processes decision-related data at different levels of granularity, and at different spatial scales, and then presents those data using SOLAP (Spatial Online Analytical Processing) tools. Spatialised indicators (action areas, pesticide types, direct costs, etc.) have been defined in close consultation with stakeholders in the field. The long-term vision for these action plans, as well as the developing needs of the different stakeholders, will allow the system to develop into a broader agri-environmental observatory storing data from the entire life cycle of successive action plans and contributing to better informed governance. By allowing for data and knowledge from stakeholder networks in multiple action plans to be pooled, the SIGPA approach is in keeping OSAGE (Loireau et al, 2017) and aims to an agro-environmental and multifunctional observatory.