A federal judge gave the Trump administration a narrow, symbolic victory on the issue of water jurisdiction, finding that its predecessor’s signature water policy violated the law.

Judge Lisa Godbey Wood’s Aug. 21 opinion found that the Obama administration’s Waters of the United States rule, also known as WOTUS, was in violation of both the Clean Water Act and the federal law that governs how agencies can make new policies.

The WOTUS rule, first implemented in 2015, was an attempt to redefine which bodies of water are subject to federal anti-pollution protections. Republicans and business groups strongly opposed the...