Eastern Highland Rim

Six permitted dischargers in the Eastern Highland Rim watershed are in Significant Non-Compliance for failure to submit required discharge monitoring reports: BASF Corporation, Reed Property, Scott's Auto Salvage and Sales, Sparta Metal Processing LLC, Tennetek Inc, and THK Rhythm North America Company. Discharge monitoring reports are the primary mechanism for tracking pollutant compliance.

Caney Fork River is designated as impaired and listed on the Clean Water Act's 303(d) list but lacks a cleanup plan. The river requires a Total Maximum Daily Load (TMDL) to establish pollution limits and guide restoration efforts.

Two Monarch butterflies were observed on September 7, 2026 at Sandy Stone Camp Rd in Monterey, Tennessee. Monarchs migrating through the region at this time are moving toward overwintering sites in Mexico, and the species is federally proposed for threatened listing.

Seven Fowler's Toads were observed on September 19, 2026 near Baxter and Window Cliffs Trail. This represents late-season activity before toads enter hibernation in September to October. The sightings likely reflect dispersal or movement toward hibernation sites rather than breeding, which typically concludes by early August.

Blue mistflower, Tall Ironweed, and Southern Sneezeweed were in bloom at Window Cliffs State Natural Area on September 19, and Swamp Goldenrod was flowering near Sparta the same day. These native fall bloomers are reaching peak flowering in response to the warm, dry conditions of the past month.

A Nashville Warbler was confirmed at Window Cliffs SNA on 2026-09-11 and reported again on 2026-09-21 across multiple checklists. The species is now in the early phase of its fall passage through Tennessee, moving from northern breeding grounds toward Mexico and Central America. Birds typically arrive in the region from early September through late October.

The region's drought has essentially broken in the span of a single month. In late May, moderate drought covered the entire area and severe drought had settled over nearly a quarter of it; by mid-July, abnormally dry conditions still gripped almost all of the landscape. Then, in just two weeks, that pattern reversed entirely: by the last week of July, abnormally dry conditions had fallen to essentially nothing, and moderate drought dropped to zero. That shift is the hydrology behind the Calfkiller's surge two weeks ago, when flow roughly doubled off its early-July low. The river is still running well above that low today at the Highway 70 gauge in Sparta, at 74.5 cubic feet per second. In a karst basin like this one, rain doesn't just raise the visible channel; it recharges the limestone seeps and springs that feed the area's caves and streams. Cave and long-tailed salamanders are known to use these cooler, saturated habitats during hot months, though how directly this particular recharge event affects their refuge conditions isn't something the available data can confirm. A drought-free basin means those underground systems are being replenished too, not just the river people can see. Worth noting plainly, though: the Sparta gauge tracks only stage and flow, with no dissolved oxygen, pH, or temperature readings over the past 90 days. So while the numbers confirm the summer squeeze has eased, whether the warm, shallow stretches that raised dissolved oxygen concerns earlier this month have actually recovered can't be checked from this data. The flow recovery is real; the water quality picture underneath it remains a gap, not a reassurance.

Giant Mayflies (Hexagenia limbata) are emerging from plateau streams this season — two confirmed sightings at Fall Creek Falls State Park on June 20 and one near Cookeville on June 3 — and that sequence of appearances is worth pausing on. These insects spend the better part of two to three years burrowed into stream sediment as nymphs, filter-feeding and respiring in conditions that would kill most aquatic invertebrates the moment oxygen dips. Their successful emergence here, at the height of summer when water temperatures peak and dissolved oxygen is at its seasonal low, is among the most reliable biological endorsements a stream system can offer. The ecology of Hexagenia makes their presence especially meaningful on the Eastern Highland Rim. The nymphs are exquisitely sensitive to fine sediment loading and nutrient enrichment — both reduce interstitial oxygen in the benthic zone where they live, effectively smothering burrows that can extend several centimeters into a streambed. A successful cohort reaching adulthood signals not just current water quality, but clean sediment conditions sustained across multiple years. Each individual that takes flight is the product of a larval tenure that began under the conditions of a previous administration, a previous flood season, a previous summer of upstream land use. The broader watershed context complicates the picture in ways that make the emergence all the more notable. The Calfkiller River was running at 205 cubic feet per second as of late June — well above the low-water stress thresholds that concentrate pollutants and drive oxygen sag in midsummer. That elevated flow provides crucial dilution and maintains the riverine connectivity that allows emerging adults to disperse. Downstream, Center Hill Reservoir remains on the federal impaired-waters list with no approved cleanup plan, meaning that the headwater streams producing these mayflies are doing ecological work that the lower system cannot yet match. The historical baseline for Hexagenia is a cautionary one. The genus was nearly extirpated across large stretches of the Midwest by mid-twentieth century eutrophication — excessive nutrient loading from agricultural runoff and municipal sewage drove the oxygen crashes that obliterated nymph populations across Lake Erie and the upper Mississippi basin. The species' famous return to Lake Erie in the 1990s, following sustained reductions in phosphorus loading, stands as one of the landmark recoveries in North American freshwater ecology and a proof of concept for what nutrient management can actually achieve at landscape scale. That recovery took decades, and the populations here on the Interior Plateau have almost certainly never faced that kind of systemic collapse — which is precisely why holding the baseline here matters so much. Each emergence season on these streams functions as a quiet, biological referendum on whether the sediment conditions upstream have held. The June timing — late, but not anomalously so — and the geographic spread of sightings across two separate drainages suggest a population that is neither thriving explosively nor in obvious distress. The next questions worth tracking: whether the emergence density holds in dry years when the Calfkiller drops into low-flow stress, and whether downstream impairment eventually works its way up through the reservoir's sediment influence into the cooler tributary reaches where these nymphs are still managing to grow.

The Calfkiller surged to 107 cubic feet per second today — nearly double the flow measured just two weeks ago in early July. For a limestone river already stressed by summer low water, this karst pulse is both blessing and fragile reprieve. The surge briefly cools the shallows where Stream Bluets and Fragile Forktails are still on the wing in mid-emergence — the dragonflies and damselflies that depend on consistent oxygen and cool water to complete their aquatic development. Common Whitetails are also active on the system. Karst drainage is relentless, however—what fills fast also drains fast. This impaired river needs a wet August to sustain breeding insects through the heat and carry them toward emergence. Without it, the ecological window closes quickly.

The Calfkiller River carries the designation of an impaired waterway—one stripped of recovery direction. For months this limestone system runs clear and complex, but come July, when flow constricts to 59 cubic feet per second and summer heat arrives, the margin between survival and collapse narrows sharply. Low flow and high temperature conspire to crush dissolved oxygen, locking out the native fishes that depend on it. Orangethroat Darters were documented here in March, proof the river still harbors its native smallwater fauna. Yet without an approved cleanup plan, there is no legal pathway to reverse the damage or prevent its deepening. The limestone geology here suggests resilience—this region holds deep groundwater reserves that could, with intentional management, sustain cooler flows and better oxygen—but resilience without action becomes only potential. The Calfkiller waits.