Surface area was measured with the “Polygon” tool from Google Earth© between the starting and ending coordinates, the back of the beach and the waterline.Litter density per 100 m was calculated as litter count * 100 / distance.Litter accumulation rates were either calculated as (1) litter count * 1000 / surface / days elapsed since the last cleaning, or (2) litter count * 1000 / surface / days elapsed since the last monitoring when no cleaning was performed, or (3) litter count * 1000 / surface / days elapsed since the last monitoring for Plastic / polystyrene pieces 0.5 and Pellets.#999.999 = accumulation rate not calculated