A method and system for detecting a floating layer on a surveillance area of the sea surface, a site of interest being placed in or around the surveillance area. The method comprises the following steps: a) satellite measurement of a radar feedback return, the radar signal being emitted by a satellite toward the sea surface of the surveillance area; b) recognition of at least one swell profile of the sea surface in accordance with the satellite measurements; c) identification of the fluid properties corresponding to the recognized swell profiles; and d) emission of a warning when the fluid properties identified for one of the recognized profiles correspond to a sea surface that includes undesirable elements for the site of interest.