The Trump Administration revealed the new and long-awaited “waters of the United States” or “WOTUS” rule last week, which is designed to clear confusion on one of the most hotly debated topics in environmental law today – the scope of federal jurisdiction under the Clean Water Act (CWA).

This rule is the second and final step in a process that began with President Trump’s February 2017 Executive Order calling on the EPA and Army Corps of Engineers to revise the definition of “waters of the United States.” The Administration sought to provide a “clear, understandable, and implementable” definition of WOTUS by clarifying the types and reducing the overall number of waterways regulated by the federal government.

The definition of “navigable waters” under the CWA has been unclear since the Supreme Court’s 2006 ruling in Rapanos v. United States, which resulted in no majority opinion. To attempt to resolve that uncertainty, the EPA and Corps issued the WOTUS rule in May 2015. That 2015 rule, which opponents viewed to improperly expand the extent of regulated waters, quickly became the subject of multiple, yet ongoing, suits. Indeed, the mix of pending cases has caused the 2015 rule to be stayed in all but 22 states.

The proposed new rule seeks to resolve the uncertainty created by Rapanos in part by specifying six categories of waters that fall under CWA jurisdiction. These categories are:

1. Traditional navigable waters;

2. Tributaries to those navigable waters, meaning perennial or intermittent rivers and streams that contribute flow to a traditional navigable water in a typical year;

3. Certain ditches, such as those used for navigation or those affected by the tide;

4. Certain lakes and ponds that are similar to traditional navigable waters or that provide perennial or intermittent flow in a typical year to a traditional navigable water;

5. Impoundments such as check dams and perennial rivers that form lakes or ponds behind them;

6. Wetlands that abut or have a direct hydrologic surface connection to another water in the U.S.

Additionally, the proposed rule expressly excludes other locations of water – including groundwater – from CWA regulation. Public comments regarding the new proposed rule will be accepted by the EPA for 60 days following its publication in the Federal Register (which is expected to occur within the upcoming weeks).

The proposed new rule is a step toward clarifying the CWA’s scope, but the drama is likely far from over. We will be watching to see if the proposed rule is modified following the agencies’ consideration of public comments and, ultimately, whether it will withstand almost certain challenging litigation.