Stormwater wetlands clean water much the same way as natural wetlands.  Wetland plants filter water as it passes through the marsh, and the chemical and biological processes unique to wetlands render many pollutants harmless, making the water exiting the wetland much cleaner than when it entered. Engineers and biologists have found ways to design stormwater treatment wetlands into our stormwater detention and conveyance systems.  These treatment wetlands are one of the very best options we have for cleaning polluted runoff.