In California Groundwater Rights Case, O’Melveny Team Achieves Resolution After Multiple Trials and Appeal

FOR IMMEDIATE RELEASE

CENTURY CITY—March 10, 2026—A team of litigators from international law firm O’Melveny & Myers LLP prevailed in a groundwater rights adjudication that approved a comprehensive plan for allocating and better managing vital water supplies in one of California’s most productive regions. While many water rights disputes have lasted decades, O’Melveny helped drive the dispute to final resolution in just seven years, including a hiatus during COVID.

On March 5, the California Court of Appeal affirmed the final judgment in a comprehensive groundwater adjudication that proceeded under California’s streamlined groundwater adjudication procedures adopted following the Sustainable Groundwater Management Act (SGMA). The watershed at issue was the 42,200-acre Las Posas Basin, a crucial irrigation source for the thirsty farms, orchards, businesses, and cities and communities in Southern California’s Ventura County.

O’Melveny represented a diverse group of landowners and farmers who rely on the basin’s water to irrigate their crops and serve their properties. “Our clients have farmed using basin groundwater for generations, and they are grateful that these issues are now settled and resolved—not only for now but going forward,” said O’Melveny partner Heather Welles, who co-led the litigation team with partners Russ McGlothlin and Matt Kline, chair of the firm’s Water Group.

The appellate opinion, which affirmed a 2023 trial court decision, shows how stakeholders, judicial authorities, and regulators can work in tandem to manage groundwater in a manner consistent with SGMA’s objectives, which took effect in 2015 and was designed to ensure sustainable management of the state’s precious groundwater resources. The O’Melveny team, formed by McGlothlin, painstakingly negotiated an equitable method for allocating and sharing the important Las Posas Basin water supply. McGlothlin successfully led negotiations to reach settlements and develop a stipulated judgment that the Santa Barbara County Superior Court adopted after three phases of trial and over objection from a handful of parties.

Kline led the trial team that defended three interim settlements and the final judgment, which was upheld on appeal last week. The Phase 2 trial in 2022 was the most contentious, lasted a month, and focused on groundwater allocation and numerous water-rights questions, including who owned the water rights that various mutual water companies have long pumped. O’Melveny served as lead trial counsel for a group representing approximately 87% of the basin’s diverse water users—more than 100 parties, including all of the basin’s public agencies and all but two of its mutual water companies. The O’Melveny team presented the court with a groundwater allocation system that balanced the needs of differently situated users and protected the basin’s water supply within the framework of California water rights law. The third and final phase of trial ended in 2023 with a capstone trial win for O’Melveny when the judge adopted a water management plan that sets the rules for future governance.

A group of dissatisfied landowners and two private water companies appealed. Last week’s 47-page, unanimous Court of Appeal decision affirmed the legality and equity of the allocation plan and its application to all parties in the Basin. “We and our clients are gratified by the decision,” Kline said. “Many diverse interests were at play, and we had to find a fair way to bring everyone to the table to find a solution. I’m grateful for the trust our clients put in Russ and the O’Melveny team to help bring this matter to closure. I’m also very proud of the hard and tireless work of our O’Melveny Water Team and clients.”

In addition to Welles, Kline, and McGlothlin, the O’Melveny team included counsel Zach Smith and Kathryn K. Turner and associate Adam Phillips.

The case is Las Posas Valley Water Rights Coalition v. Ventura County Waterworks District No. 1 et al., 2d Civ. No. B330837 (Super Ct. No. VENCI00509700).

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Contact:

Brandon Jacobsen
O’Melveny & Myers LLP
+1 213 430 8024
bjacobsen@omm.com

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