The U.S. Environmental Protection Agency says more than half of rivers and streams in the United States are in such unhealthy shape they cannot adequately support aquatic life. EPA sampling found more than 55 percent of waterways tested were in poor condition, compared to just 21 percent in good health. The most widespread cause was pollution fueled by human activity, with high levels of phosphorus — a component of fertilizers, pesticides and detergents — found in 40 percent of rivers and streams.