North Fork Coles Creek

North Fork Coles Creek, which the Natchez Trace Parkway crosses near milepost 25.7 in Jefferson County, had been listed as impaired more often than any other stream the parkway crosses when the Park Service assessed them in 2014. The Park Service's 2014 natural resource condition assessment counted eight listing cycles since 1996, the latest for biological impairment, more than for any of the twenty impaired streams the parkway crosses. About five miles west-southwest of the crossing the fork becomes Coles Creek, which drains its own basin westward to the Mississippi River.

The streams of that basin are the warmest the parkway's monitoring records. At the three stations sampled there, on the North Fork, the South Fork and Mud Island Creek, summer water regularly exceeded the state maximum temperature. The assessment puts that down to natural conditions: these are the southernmost stations on the parkway, and probably shallow and slow-moving because of the lie of the land. Their pH ran at the high end of the parkway's range while staying within state standards. E. coli counts were often high, mostly in the colder months, though only the North Fork exceeded the state limit.

Fish were sampled thinly, three summer collections inside the park that averaged seven species apiece, with tolerant species making up 42 percent of them, and the assessment rated the assemblage fair. Even so, the Coles Creek reporting area held a relatively high share of species found in no other reporting area along the parkway. Mud Island Creek, crossed near milepost 21, joined the North Fork on the impaired list in 2010.