This week the City of Dayton began work to replace the Helena Street Bridge over the Great Miami River. The project is expected to take more than a full year to complete, and it does close a small portion of the Great Miami River Trail in Dayton.
Fortunately - no detour is needed to get around this closure, because the trail is on both sides of the river at this point.
If you are passing through Dayton along the Great Miami River Trail you can simply bypass the closure by sticking to the east side of the river. That side could also be called the "downtown side," the "RiverScape side," or the "river-left side."