The majority of the nation’s wetlands where many birds raise their young, congregate in winter, and rest during migration—and which filter out pollutants and buffer communities from flooding and storm surges—lost legal protections on Thursday in a Supreme Court ruling that significantly curtails the reach of the Clean Water Act. That 1972 law made it illegal to drain, fill, or pollute “waters of the United States” without a permit. The case, Sackett v. Environmental Protection Agency, involved defining which water bodies that phrase applies to. Disagreement has prevailed for decades, with environmentalists arguing for broad protections to safeguard water quality and ecosystems, while builders, manufacturers, and others contend that including more streams and wetlands drives up project costs and infringes on property rights. In the 5-4 majority opinion, conservative Justice Samuel Alito wrote that wetlands are covered by the law only if they have a “continuous...