Most recently our landscape is covered by agriculture (see land cover maps below).
Figure 2. Ohio Land Cover. http://wwwapp.epa.ohio.gov/dsw/nps/NPSMP/photos/ohio_94.jpg
This in part obviously affects nature itself but also rivers in Ohio. For example here today farm runoff from the fertilizer has affected and contaminated the Ohio River.
Figure 3. Waves from Lake Erie and its impact on Ohio's coastal erosion. http://geosurvey.ohiodnr.gov/lake-erie-geology/erosion-and-research/erosion-problems