Fluid flow enhancing devices disclosed herein are adapted to enhance flow of fluid through subsurface watershed conduits, for example, culverts, drainpipe and the like. Such fluid flow enhancing devices advantageously enhance watershed runoff functionality in subsurface watershed conduits by altering watershed flow from a parabolic flow pattern to a rotational flow pattern while still accommodating fish passage requirements. This change in flow pattern beneficially provides turbulence that disrupts and flushes debris out of the subsurface watershed conduits. This disruption and flushing establishes a passive cleaning functionality within the subsurface watershed conduits that serves to clean the subsurface watershed conduits after suitable upstream water delivery event (e.g., heavy rain, controlled water release, etc.). In doing so, these fluid flow enhancing devices overcome one or more shortcomings associated with subsurface watershed conduits in a manner that overcomes drawbacks associated with conventional design and in-use considerations for such subsurface watershed conduits.