French Creek flows 117 miles from its headwaters in New York and is treasured for its remarkable biodiversity, with 27 species of freshwater mussels, more than 80 species of fish including 15 species of darters, and a healthy population of Eastern Hellbender salamanders, Pennsylvania's state amphibian. It is fed by 10 major tributaries with their own watersheds, whose surrounding land conditions are important to the creek's water quality and overall health. The nearest sub-basin here is Little Sugar Creek, which flows 12 miles south from the Guys Mills area and enters French Creek at Cochranton. The entire Little Sugar Creek sub-basin is classified as a cold water fishery supporting 15 species of fish and six species of freshwater mussels. Mud Run, a tributary of Little Sugar Creek, is one of two streams that were dammed to form Tamarack Lake.