Trawling can be divided into bottom trawling and midwater trawling, depending on how high the trawl (net) is in the water column. Bottom trawling is towing the trawl along (benthic trawling) or close to (demersal trawling) the sea floor. Bottom trawling is an industrial fishing method in which a large net with heavy weights is dragged across the seafloor, scooping up everything in its path. Bottom trawling can be disadvantageous because it stirs the sediments that lie on the sea bed and can harm some marine species. It also causes water pollutants to mix with some plankton, which in turn will move into the food chain, which will then create harmful algae blooms leading to insufficient oxygen.