Agricultural best management practice (BMP) adoption has the benefits of controlling and reducing agricultural non-point source pollution. To facilitate the adoption, adequate information needs to be provided to farmers and conservation managers to improve their understanding on BMPs and support their decision making on BMP adoption. By utilizing information and communication technologies, this study introduces the design and implementation of a WebGIS-based decision support system to fulfill the information needs of farmers and conservation managers for BMP adoption. In the first step, this study develops an information model that conceptualizes information communications within the BMP adoption process. The information model specifies the information content for communications as well as defines how information could be generated and communicated to meet the information needs of farmers and conservation managers, which are classified into public information and BMP planning information based on the accessibility of information. Based on the information model, this study designs a WebGIS-based decision support system for facilitating agricultural BMP adoption which includes three subsystems: the public subsystem for supporting communications of landscape conditions and BMP educational information, the BMP planning subsystem for supporting communications of BMP planning information, and the administration subsystem for supporting administrative tasks including monitoring the use of the BMP planning subsystem by farmers and conservation managers. Based on the system design, a prototype of the WebGIS-based decision support system is developed for the Gully Creek watershed, which is a representative watershed in southwestern Ontario with active agricultural BMP implementation activities. The system prototype is then evaluated by two methods: evaluation by direct use and evaluation during demonstration. The evaluation by direct use identifies violence to usability principles, while the evaluation during demonstration focuses on evaluating user task and information of the system. The results from the two evaluation methods are coded into the evaluation measures and aggregated for conducting an assessment of the system usability. The results show that the evaluators are overall satisfied with the system design and functionalities. Several suggestions on further improvements to the system are also provided.