Bottom trawling stirs up the sediment at the bottom of the sea. The suspended solid plumes can drift with the current for tens of kilometres from the source of the trawling, increasing sedimentation rates in deep environments Bottom trawling-induced resuspended sediment mass on the world's continental shelves have been estimated to approximately 22 gigatonnes per year, approximately the same as the sediment mass supplied to the continental shelves through the world's rivers. These plumes introduce a turbidity which decreases light levels at the bottom and can affect kelp reproduction.