The Waters of the United States rule was created after the Obama Administration shifted through more than a thousand scientific papers to identify which streams, creeks, and wetlands were relevant to environmental health.

The rule was lauded as a big step forward for ocean health. However, few expected it to cause so much controversy—poor public understanding led to widespread perception that the rule covered more than it did, and it became a lightning rod for conservatives.

Trump is empowering new EPA head Scott Pruitt to undercut the rule, leading to fears that the rivers leading to the sea will be vulnerable to pollution.