rotting algae on dark water

alga algae aquatic biomass blanket blanketed blanketweed bloom blooming bubbles canal choking contamination dark dense deoxygenate deoxygenating depletion dirt dirty disgusting ditch duckweed environment eutrophication floating gas green lake layer leaves lemna methane nature nutrients organic oxygen plant polluted pollution pond rotting scum slime stagnant stinking suffocate suffocating surface thick vegetation water waterweed weed weeds