Trends in WOTUS and why we continue to see litigation on the U.S. Clean Water Act

The Clean Water Act is complicated, and these complexities have been magnified by Supreme Court cases seeking to answer, "what is regulated?" Debate about which streams, lakes, and wetlands are regulatory (hereafter the "Waters of the United States", or WOTUS) has regularly arisen since the term was originally included in the 1972 amendments. A permit is required before dredging, filling, or discharging pollutants to WOTUS, so it is important to understand the geographical extent of legal protections. Despite the clear importance of understanding which waters are federally regulated, numerous court decisions and agency recommendations have not produced a robust definition required for proactive and efficient regulation. Moreover, while several comprehensive reviews discuss the evolving legal definition of WOTUS, these do not translate to a practical assessment of how the scope of the Clean Water Act is changing on the landscape.

Our objective in this study is to document the evolving spatial protections afforded to U.S waters from 1948 to present. We examined how the implementation of the act has evolved as it has been influenced by amendments, Supreme Court cases, executive orders, and agency rules during its 72 year history, at the time of publication. Based on the evolution of the regulatory process, we quantified the impact these changes have had on the ground, detailing the miles of stream, and acres of lake and wetland regulated from 1948 to present day, taking the Wabash River basin as a case study. We highlight key decision-points and their on-the-ground consequences, and attribute quantitative bounds to the vague and uncertain terminology. This quantitative history of WOTUS is the first of its kind and serves to document the co-evolution of enforcement with our understanding of hydrological systems, detail trends in regulatory scope, and provide historical context for ongoing debates about the enforcement of the Clean Water Act.