research community is witnessed by many projects and prototypical systems for marine pollution monitoring [4; 5]. Recent works include cloud-based solutions [6], in which a cloud-based image processing facility for oil spill detection is integrated with a web-based geographical information system, and the framework introduced in [7], in which a fine-grained hydrodynamic model is used for accurately forecasting oil spill evolution and weathering. The main contribution of this work is to propose an integrated and interoperable system based on advanced sensing capabilities yet suitable for local authorities and stakeholders in order to monitor, detect and provide adequate response also to medium and micro oil spills. To this end, we adopt the Marine Information System (MIS) presented in [8], which integrates Synthetic Aperture Radar (SAR) processed data, environmental data from in situ monitoring stations (e.g., sensorized buoys [9]) and dynamic data acquired from Autonomous Underwater Vehicles (AUVs). With respect to previous works--mainly pivoting on SAR images--the MIS introduced in [8] has shown that remote sensing can be effectively enriched by adding information collected in situ thanks to static and mobile sensors and leveraging innovative methods for data correlation and fusion. Besides the integration of the above information coming from authoritative sources, the contribution of this work is the integration of Volunteered Geographical Information (VGI), aiming at a more pervasive monitoring of the sea thanks to citizen science. Starting with the seminal work by [PERSON] [10], VGI has been proven to provide useful information in the case of events like hurricanes, earthquakes and pandemics. The contribution of the public can be determinant in giving to authorities and stakeholders near real-time information and nowcasts for facing emergencies in a timely manner. This new way of producing geographic information brings up new potentials together with many issues as highlighted in [11]. Crowd-sourced information is extremely powerful, but at the same time, requires substantial changes to the conventional information chain by intertwining authoritative and non-authoritative data [12]. In this context, our contribution aims at properly integrating VGI for improved monitoring of oil spills. Notice that the use of VGI for water monitoring and security is rather new and is experiencing a period of increased interest. Pioneering works such as [13; 14] have shown the capability of VGI in connection with the monitoring of streams and with the preservation of their biological richness. The fitness for use and the limits of VGI are analytically discussed in [15] for flood damage estimation; it is shown that VGI can be a great opportunity for water monitoring and disaster management, although quality control methods are envisaged to be essential for fully deploying this potential. More recently, [16] proposed a crowd-sourced information system devoted to vessel tracking for interpreting maritime traffic in an ecological context; the system is capable of providing a spatially-resolved dataset, which put in relation individual ships with their mobility patterns and vessel attributes by incorporating quality checking methods with volunteered geographic information. In [17], a Geographic Information System (GIS) solution is developed using a VGI approach to reduce the burden associated with collecting and managing marine mammal observations. Suitable web and mobile applications are made available for the general public to submit marine mammal observations and visualize the results. In [18], the utility of citizen science in cetacean research and marine spatial management has been assessed. A new data source on whale locations, observation data collected voluntarily by whale-watching vessels, is procured, compiled and digitized.