The Trump administration today stripped protections from most wetlands and millions of miles of streams, ignoring warnings from its own scientists that these modest waterways are essential sources of clean water and wildlife habitat. The 1972 Clean Water Act made it illegal to drain, fill in, or pollute the “waters of the United States” without a permit, but exactly which waterways that broad definition included has been the source of legal disagreements ever since. The Obama administration sought to clarify matters in 2015 with its Clean Water Rule, sometimes called WOTUS for Waters of the United States. Real estate developers, farmers, and others complained that the Obama rule, which encompassed about 60 percent of the nation’s waters, was too strict, requiring them to seek costly permits for routine operations. Last September, the Trump administration threw the new rule out and reverted to an earlier interpretation of the act. Today’s replacement, called the...