CleanSeaNet detections can be caused by mineral oil but may also indicate other pollutants (e.g. sewage, garbage) or naturally occurring features (e.g. algae blooms, areas of upwelling, etc.). Additionally, not all oil spills detected by CleanSeaNet are illegal (e.g., discharges outside of special areas, with oil content less than 15 parts per million and located more than 50 nautical miles from shore). In connection herewith it should also be mentioned that permitted discharges of oil with produced water from offshore oil & gas installations in certain weather conditions can give rise to accumulation of oil sheens at the sea surface. CleanSeaNet detections require further validation / confirmation by the Member States as part of their surveillance and enforcement activities.