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.

Scientists tested the delicate ecosystems of the Marianas Trench and found highly elevated levels of PCBs, which were banned in 1977 in the United States as a threat to public health.

At the same time that oceans are taking in massive amounts of carbon dioxide, they're absorbing less oxygen than ever.

The top levels of the ocean are warmer than usual thanks to human-caused climate change. That is leading to an expansion of oxygen-poor hypoxic zones. Fish don't live in those. Large fish, in particular, are threatened by ocean oxygen loss, with the Pacific and Arctic experiencing the steepest declines.