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Iowa's Low Hanging Fruit

Stream Buffer Rule = Cleaner Water, Little Cost

The Five Counties

February 3, 2015

Iowa's Low Hanging Fruit: The Five Counties

Rather than take on the task of assessing every waterway in Iowa, EWG picked five counties – Allamakee, Hamilton, Linn, Plymouth and Union – chosen to reflect each of Iowa’s five major landscape regions (Figure 1).

Figure 1: The five counties are in each of Iowa’s major landscape regions.


We also selected these counties so as to reflect the wide county-to-county range in the percentage of land devoted to row crops (Table 1). For example, Hamilton County, in the center of the Des Moines Lobe landform, is almost entirely cultivated, while farming is far less prevalent in Allamakee County in northeast Iowa’s Paleozoic Plateau because of the region’s karst topography.

Table 1: Prevalence of row crops and miles and number of stream assessed in each county

County Percent of Land in Row Crops Stream Miles Assessed Number of Streams Assessed
Hamilton >80% 280 30
Plymouth >70% 400 28
Union >60% 270 24
Linn >50% 430 40
Allamakee >20% 362 38

EWG limited its assessment to named waterways in the US Geological Survey’s National Hydrography Dataset (NHD) in order to focus as much as possible on perennial waterways. Of the total of 1,742 stream miles across the five counties (Table 1), 81 percent are perennial, 15 percent are intermittent and 4 percent are ditches. For intermittent streams and ditches, we limited our assessment to those segments that have defined beds and banks.