This long and relatively narrow watershed spans three counties and varies greatly in terms of the physical landscape, soils, and amount of annual rainfall.

The middle portion is nearly flat with a river gradient of only five feet per mile (see the river profile and river gradient map). This relatively flat gradient is different from the steep upper and lower reaches of the watershed. Generally, the upper, western portion of the watershed is drier and receives four inches or less rainfall per year on average than the lower portion of the watershed (precipitation map).

In the middle watershed, the river widens, slows down, and meanders through a large floodplain with vast areas of grasslands, wetlands, and pastures. Nitrogen and phosphorus are often reduced by more than 50 percent in this stretch of the river because of the natural filtering processes common in these types of environments. However, fecal coliform bacteria levels are highest in this area (near Monitoring Site #3). The high bacteria levels may be due to the number of feedlots in this area, as well as the open access that livestock have to the river because much of the floodplain is used as pasture.

Soils also vary across the watershed. (See the soil survey map, and soil erosion potential maps: (upper, middle, lower), which illustrate this variability. Next