Good EPA "laws" (read: "rules", "regulations") are long extinct, but if you had to pick one it would be the 1972 Clean Water Act (CWA) passed by congress four years after the Cuyahoga River in Ohio caught fire (Images for cuyahoga river fire burning--it wasn't the first time) because of the pollution in it.
The Act authorized the clean-up of this kind of mess in America's navigable lakes, rivers, and streams, and prohibited further dumping of dangerous industrial chemicals, waste, and other byproducts into these bodies of waters. It also allowed states to manage the clean-up of their own waters under the Clean Water Act (CWA), and enabled federal and state officials to work together to get the job done, .