President Donald Trump sought to shrink the law's reach in his first term while prior Democratic administrations have expanded federal power to regulate the nation's lakes, rivers, streams, wetlands and oceans. That's created drastic swings in how the law is interpreted and applied.

The Environmental Protection Agency (EPA) has signaled that it could narrow which set of waters receive protections under the Clean Water Act. The law requires the EPA to protect so-called “waters of the United States” but there has been significant political back-and-forth as to which bodies of water that should include.