The article discusses how nonpoint source pollution is a major threat to America's water quality. The focus is on the Total Maximum Daily Load (TMDL) program, which sets limits on pollutants in water bodies. The researchers found that NPS pollution is the main reason why many waters don't meet quality standards. TMDLs act like a recipe, determining the maximum amount of pollutants that can be present in water while keeping it healthy. States need to identify pollutants in water and calculate how much each source can contribute to the pollution.