Rolling Loess Prairies

Most of the named surface waters around the Rolling Loess Prairies are already living under a pollution diet. EPA's 2024 impairment listings show seven of the seventeen water bodies assessed within ten miles of this landscape are officially impaired under the Clean Water Act: Walnut Creek and an unnamed tributary, two segments of Little Bear Creek, Arbor Lake, and Rock Creek Lake, all five already carrying a completed TMDL, a mandated cleanup plan capping how much pollution the waterbody can absorb and still meet standards. The North Skunk River is also listed as impaired, for a non-pollutant cause.That backdrop matters because two municipal wastewater treatment plants sit right at the center of this landscape: the City of Grinnell and the Grinnell City STP. Both hold active discharge permits, and EPA's compliance record shows one currently has an unresolved permit violation, the other a violation logged within the past four quarters. Neither plant appears on EPA's significant non-compliance list, and no penalties have been assessed, zero dollars total, so the violations remain minor by regulatory standards, with no detail on which pollutant or concentration surfacing at this level of reporting.This isn't evidence that the two plants caused the downstream impairments; the TMDLs in place address other pollution sources too, and they predate this compliance record. But it is a live, unresolved compliance flag sitting immediately upstream of a watershed where seven of seventeen named creeks and lakes are already under mandated cleanup, a coexistence worth watching rather than ignoring.

Trumpeter Swan (Cygnus buccinator) was sighted near Marshalltown on July 4th — a species entirely absent from Iowa for most of the twentieth century, hunted out by the late 1800s and now returning through decades of careful reintroduction from remnant populations in the upper Midwest. Its presence here is a measure of how far this recovery has come.Midsummer is molt season for trumpeter swans. Their flight feathers regrow over several weeks, and during that flightless stretch they become entirely dependent on stable water and dense vegetation for protection. The current streamflow is just over 12 cubic feet per second — a near-record low following two weeks of drought that succeeded July's earlier storms. These conditions shrink the shallow wetland margins where molting birds shelter and feed, leaving them exposed and unable to move elsewhere even if conditions worsen.One bird in early July, in a drought year, might seem like a small thing. But in a region where deep wetlands remain thin on the ground, it signals that the slow, deliberate work of restoring this species to central Iowa is holding, even under stress.

In the span of two weeks this summer, streamflow here plummeted from over 2,100 cubic feet per second down to under 21—a swing of more than one hundredfold in either direction. The trigger was simple: late June's dry spell followed by July's storm.What's striking is the speed. Before European settlement, rolling loess prairie dominated this landscape—dense root systems that worked like a sponge, slowly absorbing summer rain and releasing it steadily through the growing season. That natural buffer is gone. Today's row crops shed water almost instantly, sending it racing downslope into streams that are already warm and nutrient-rich—conditions tailor-made for algal blooms. The timing of peak flow hitting the warmest, most algae-prone moment of the year is no accident; it's how the landscape now works.