A vessel has a compartment (34) for containing water, which compartment (34) has at least one opening (31) in a wall (30) thereof for allowing water to pass therethrough. The compartment (34) comprises an assembly (1) of a grating (10) and at least one anti-biofouling source (20), the grating (10) being positioned in the opening (31) for blocking items from passing through the opening (31) along with the water, and comprising a number of elements and spaces between the elements, and the anti-biofouling source (20) being configured to emit ultraviolet light during operation thereof for realizing anti-biofouling of at least a portion of the grating (10). At least one of the elements of the grating (10) is at least partially transparent to the ultraviolet light, enabling a design of the assembly (1) in which anti-biofouling of the entire grating (10) may be guaranteed.