Pollution sources such as factories, sewage treatment plants, power plants, airports, and feedlots routinely dump pollutants into surface waters, legally and illegally. EPA announced Jan. 25, 2012, that it has unveiled a user-friendly tool for understanding and analyzing these discharges from point sources. The agency consolidated data from a number of inventories, making it easier to see who is dumping what, when, and where, and who is known to be in violation of their permit.
- Discharge Monitoring Report Pollutant Loading Tool  (includes extensive information on how to use it); press release. 
The data cover 2007-2010. There are some information shortcomings — such as the absence of nonpoint sources and certain types and sizes of facilities, and differences among states in what and how comprehensively they report — but the available data can give you a good head start on investigating national and local waterway contamination.
You can sort and rank the results according to categories such as type of pollutant, mass, and toxicity, and find out the biggest culprits in your audience area. In addition to specific national, regional, or local impacts, the results can help you explain why such a high percentage of US waterways remain unacceptably dirty for their intended use (such as drinking water, fishing, or recreation), leaving the country far short of meeting the 40-year-old goals of the Clean Water Act.
For instance, a 2006 report found that 42% of wadeable streams were in poor condition. An update is scheduled for December 2012.
A 2010 report on lakes, based on a limited number of criteria, found that 22% of them are in poor condition, 36% have poor lakeshore habitat, and 49% exceed the health-based limit for mercury in game fish. An update, based on sampling at 904 lakes, ponds, and reservoirs this summer in the lower 48 states, is expected in 2014.
For more information and data on these problems, resources include: