Designated on June 22, 1984, and October 3, 1994; 82 miles total.
- Big Darby Creek from the Champaign-Union County line downstream to the US Route 40 Bridge, from the northern boundary of Battelle-Darby Creek Metro Park to the confluence with the Little Darby Creek downstream to the Scioto River.
- Little Darby Creek from the Lafayette-Plain City Road Bridge downstream to the confluence with Big Darby Creek.
The Darby Creek system constitutes some of the most important natural resources in central Ohio.
Flowing through rich agricultural bottomland of Union, Madison, Franklin and Pickaway counties, the creek's valley ranges from gently rolling topography in the upper reaches to relatively steep and heavily wooded land in the lower portions. Both streams were included in the national scenic rivers program in 1994.
Big and Little Darby Creeks are noted nationally for their tremendous diversity and abundance of both aquatic and terrestrial plants and animals. They are home to 86 species of fish, five of which are endangered in Ohio including the federally endangered Scioto Madtom, which is endemic to the area.
Forty-one species of freshwater mollusk live in these waters, eight of which are on the Ohio endangered list. The Darby Creek watershed covers an area of 556.6 square miles.
The creeks' banks are flanked with native vegetation varying considerably in width; from only a narrow line of trees to deep and extensive forests. Floodplain trees such as buckeye, sycamore, silver maple and box elder tolerate periods of inundation. Species more adapted to drier soils such as oak and sugar maple line the valley walls.
Remnant prairie species — purple coneflower, the threatened prairie false indigo and Indian paintbrush — inhabit the slopes and bluffs along the streams. Numerous species of birds and mammals depend upon this linear strip of undisturbed habitat for their existence.