A stormwater filtration system includes a stormwater containment structure including a concrete floor and a pre-assembled flow structure embedded in the concrete floor. The pre-assembled flow structure includes an inlet compartment housing, an outlet compartment housing and at least one filter conduit positioned between the inlet compartment housing and the outlet compartment housing and in flow communication with the interior of the outlet compartment housing. At least one bypass conduit extends from the inlet compartment housing to the outlet compartment housing for delivering water from the interior of the inlet compartment housing to the interior of the outlet compartment housing. A plurality of filter units are connected to the filter conduit so that stormwater filtered by the filter units passes into the filter conduit and then to the interior of the outlet compartment housing.