O’Melveny Worldwide

Heather Welles pairs litigation and appellate success at the highest levels with substantive expertise in water, a field of growing importance to even the largest companies. A diverse set of clients, including innovative farmers, major movie studios, large water districts, champion athletes, skin-care pioneers, private equity funds, and environmental conservation and recreational organizations rely on Heather to write case-winning briefs, develop persuasive legal theories, and creatively resolve disputes.

Heather’s briefs have repeatedly carried the day in federal and state trial and appellate courts and arbitrations, including merits, certiorari, and amicus briefing at the US Supreme Court. She has briefed subjects including federal and state constitutional law, federal courts and jurisdiction, statutory interpretation, water law, land use, public trust, contracts, administrative law, and trademark law. A founding member of O’Melveny’s formal water practice, Heather regularly speaks on water issues, including guest lecturing at Harvard, NYU, and UCLA law schools. Heather also maintains an active pro bono practice focused on civil rights and impact litigation.

In 2023, Law360 recognized Heather as a Rising Star, one of six top attorneys under 40 nationwide in environmental law. In 2022, the Daily Journal recognized Heather as one of the forty top lawyers under the age of 40 in California, highlighting her water work and appellate practice.

Prior to joining O’Melveny, Heather served as a law clerk for the Honorable David S. Tatel on the DC Circuit Court of Appeals and the Honorable William A. Fletcher on the Ninth Circuit Court of Appeals.

Heather graduated from the University of California, Berkeley School of Law, where she was awarded the Thelen Marrin Prize for Academic Excellence for graduating first in her class and served as the Editor in Chief of the Ecology Law Quarterly. She previously served as a legislative director in the Texas House of Representatives, where she worked on groundwater regulation, water quality, energy, and land use.

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Representative Water and Natural Resources Matters

  • Agua Caliente Band of Cahuilla Indians v. Coachella Valley Water District. Representing Coachella Valley Water District in federal court on multiple matters of first impression involving reserved water rights, including successfully obtaining dismissal of several claims on standing grounds at summary judgment.
  • Las Posas Water Rights Coalition v. Fox Canyon Groundwater Management Agency & OPV Coalition v. Fox Canyon Groundwater Management Agency. Representing coalitions of large landowners in the first comprehensive groundwater adjudications under California’s groundwater management and adjudication statutes. 
  • California Resources Corp. v. County of Monterey. Primary author of appellate briefing successfully defending a challenge to a local initiative impacting property rights and water use. Also obtained rare regulatory takings victory at bench trial as the primary brief drafter for the trial team and presented argument at trial and in collateral administrative proceedings.
  • Advising on water rights and legal issues affecting water supply in multiple contexts, including disputes, major transactions, project development, governance, and regulatory compliance. Representative projects include multi-million-dollar transactions related to land and water rights acquisition and infrastructure development.

Representative Appellate Matters

  • City of Austin v. Reagan National Advertising of Texas Inc. Successfully represented the City of Austin at the US Supreme Court in a First Amendment dispute over billboard regulations, including obtaining certiorari and a favorable decision on the merits reversing the Fifth Circuit.
  • Chama Troustalkers, LLC v. Adobe Whitewater Club of New Mexico. As counsel of record, successfully opposed certiorari in a case that protected public recreational use of non-navigable waters throughout New Mexico.
  • Padilla Ortiz v. Garland. Briefed and secured a rare victory on the papers at the Ninth Circuit in an immigration case, obtaining relief for a young woman seeking asylum.
  • Shoop v. Twyford. Primary author of amicus brief representing federal courts scholars in a habeas corpus case involving an order for medical testing issued under the All Writs Act.

Representative Litigation and Counseling Matters

  • Successfully representing Warner Bros. in several important matters, including multiple contract disputes over digital cinema financing, litigation over financing participation rights involving claims exceeding US$120 million, and counseling on COVID-19-related issues.
  • Representing a health insurer in Administrative Procedure Act litigation against the US Department of Health and Human Services challenging a Medicare audit regulation.
  • Served as the primary brief writer for a successful trial team defending a renowned dermatologist and his company in a contract and trademark dispute involving claims exceeding US$80 million.
  • Served as the primary brief writer in a contract dispute defending a renowned boxer and his promoter.
  • Counseling a prominent green-buildings company on First Amendment issues.
  • Represented Planned Parenthood Arizona and individual clinicians in litigation challenging statutes that reduce access to reproductive health care.


Bar Admissions

  • California

Court Admissions

  • US Supreme Court
  • US Court of Appeals, Ninth Circuit
  • US District Court, Central District of California


  • University of California at Berkeley, J.D.: Thelen Marrin Prize for Academic Excellence (best academic record in graduating class); Order of the Coif; Editor in Chief, Ecology Law Quarterly; Landis Prize (most accomplished research paper in water or local government law); American Jurisprudence Awards for best exam in Constitutional Law, Contracts, Water Law, and Land Use Law
  • University of California at San Diego, B.A., Political Science 

Honors & Awards

  • Named a “Rising Star” in Environmental Law by Law360 (2023)
  • Recognized by the Daily Journal's 2022, "Top 40 Under 40"
  • Member of the team recognized as Environment/Natural Resources Litigation Firm of the Year by Benchmark Litigation California (2019)

Professional Activities


  • The Honorable David S. Tatel, US Court of Appeals, District of Columbia Circuit
  • The Honorable William A. Fletcher, US Court of Appeals, Ninth Circuit


  • “Toward a Management Doctrine for Texas Groundwater,” Ecology Law Quarterly, Vol. 40 (2013)
  • “What’s a Smelt Worth?: The Endangered Species Act and the Commerce Clause in the Bay-Delta,” Ecology Law Quarterly, Vol. 39 (2012)
  • “Will the Wilderness Act Be Diluted in Drakes Estero?” Ecology Law Quarterly Currents (Aug. 26, 2012) (co-authored with Nell Green Nylen, Elisabeth Long, Mary Loum, Dan Carlin, Brynn Cook, and Sage Adams)


  • “No Stone Unturned: Securing Water for a New Era,” USC Gould School of Law’s 2024 Real Estate Law & Business Forum (February 2024)