The hydraulic residence time (HRT) in each of the
open water zones should be limited to about three
days at design flow to prevent the re-emergence of
algae. Such systems should always start and end
with shallow emergent vegetation zones to ensure
retention and treatment of particulate matter and to
minimize wildlife toxicity in the open water zones.
The use of FWS constructed wetlands has increased
significantly since the late 1980’s. The systems are
widely distributed in the United States and are found
in about 32 states.