If fill is placed or building is constructed in the floodway, the permitting is more complicated and has to be approved by the Federal Emergency Management Agency (FEMA). Normally, encroachments into the floodway are not allowed; however, in the case of the Farnsworth house, the land across the river is state park land, and there is little development in the area. Fill in the floodway may be allowable if it can be demonstrated that the fill will not cause a rise on any insurable structure. Studies are needed to look further upstream to determine what other structures could be potentially affected.

If working in the floodway is determined to be the best approach, extra time will be scheduled for special permitting, conditional letters, surveying, and erosion management.