Various air and water pollution issues in the US were confronted in the last 60 years using national policy legislation, notably the Clean Water Act (CWA) and the Clean Air Act (CAA). Notable focal points were the concentrations of bacteria, oxygen, lead, and sulphate which are discussed here for the terminus of the Mississippi River, the dominating source of N, P and water into the Gulf of Mexico. Microbial concentrations increased or were stable from 1909 to 1980 but decreased about 3 orders of magnitude after the 1970s, while the average oxygen content increased. Lead concentrations declined after the 1960s, along with a less dramatic decline in sulphate concentrations. The pH of the river dropped to a low of 5.8 in 1965 as sulfur dioxide emissions peaked and averaged 8.2 in 2019 after emissions declined. The surge in other chemicals added each year is daunting whose stocks and transformations need monitoring, minimization and even prohibitive actions, including alkalinity and nitrate that are coupled to ocean acidification, coastal hypoxia, and climate change.

It is far better to prevent damage, of course, than fix later. The promulgation and acceptance of the CWA and CAA demonstrate how public policy can change for the better for everyone who is demonstrably ‘downstream’ in a world of cycling pollutants.