[bluGill]

While city folks like to blame farmers for the problems in Iowa, the soil in Iowa naturally makes nitrates which runs off into the streams after every rain. We have death reports from the early 1800s that on rereading with a modern eye make it clear that the problem was drinking water with high nitrates. This is both what makes Iowa such great farm country, and what makes streams harmful.

Not that fertilizer isn't making things worse (though sometimes it makes things better - farmers don't want their expensive fertilizer to wash away and so look for ways to keep it on the field), but it isn't the whole story.