The oil and natural gas industry reacted favorably to the Trump administration’s delivery on a promise to reduce environmental oversight of U.S. waters by issuing final rules Thursday that are certain to draw litigation.

The U.S. Environmental Protection Agency (EPA) and the Department of Army finalized the Navigable Waters Protection Rule to define “Waters of the United States,” aka WOTUS, which establishes federal authority under the Clean Water Act.

The new rule, scheduled to take effect two months after it is published in the Federal Register, is the second of a two-step process to review and revise the definition of WOTUS, which was ordered by the Trump administration through an executive order in early 2017.

The revisions would undo actions undertaken not only by the Obama administration but by revisions that predated Obama’s tenure. For example, more than half of U.S. wetlands would no longer qualify for federal protections.

The first step was published last fall.

“For the first time, the agencies are streamlining the definition so that it includes four simple categories of jurisdictional waters, provides clear exclusions for many water features that traditionally have not been regulated and defines terms in the regulatory text that have never been defined before,” EPA noted.

Under the final Step 2 rule, four categories of waters to be federally regulated are territorial seas and traditional navigable waters; perennial and intermittent tributaries to those waters; some lakes, ponds and impoundments; and wetlands adjacent to jurisdictional waters. The final rule also details 12 exclusion categories, “such as features that only contain water in direct response to rainfall (e.g., ephemeral features); groundwater; many ditches; prior converted cropland; and waste treatment systems.”

EPA said it received more than 6,000 recommendations and 620,000 comments on the proposal from a wide range of stakeholders.

The U.S. Chamber of Commerce’s Global Energy Institute (GEI) praised the final rule.

The announcement “brings us a step closer to clean water regulations that are clear and consistent,” GEI President Marty Durbin said. “The new rule distinguishes between waters that are regulated by the federal government and those that are regulated by the states, making it easier for businesses, states and local governments to understand their obligations.”

Lawsuits are expected, which could delay implementation.

The Public Employees for Environmental Responsibility earlier this month called for a formal investigation by the EPA Office of Inspector General into the rulemaking process, claiming it was based on politics more than science.