OBSenMER is a collaborative platform that facilitates the capture and analysis of observations at sea. It concerns all types of observations including marine mammals, sea turtles, fish, birds, but also human activities, such as boating, fishing , pollution, etc. OBSenMER is aimed at both the general public and professional naturalist structures, and collects both participatory science data and data from an expert protocol. OBSenMER is a network of collectors and users of data at sea who share tools: a mobile application, a web platform, a database, and a photo-identification tool.