Diablo Canyon and the Clean Water Act: Can You Break the Rules Until You Shut Down?

Does anyone really think Congress meant for a power plant to run its entire lifespan without following the law—just because it might shut down someday? That’s the uncomfortable question at the center of a growing legal fight over Diablo Canyon Nuclear Power Plant, and the challenge The Otter Project and California Coastkeeper Alliance just filed with the State Water Board.

When Congress passed the Clean Water Act more than 50 years ago, it didn’t mince words. Power plants must install technology to minimize marine life mortality when intaking seawater for cooling purposes. That means facilities are required to reduce harm as it occurs—not delay compliance, not substitute payments for prevention, and not promise to fix the damage later. The idea that ongoing ecological harm can be offset at some future date is exactly what the law was designed to prevent.

In February 2026, regulators reissued a permit allowing Diablo Canyon to continue operating without installing technology to reduce marine life mortality. The justification rests on two assumptions: that the plant may retire at some speculative point in the future, and that mitigation payments can offset the environmental harm in the meantime.

This raises a fundamental legal question: can a speculative future event substitute for present compliance with federal law? Under the Clean Water Act, the answer should be no.

Diablo Canyon, operational since 1985, stands as the single most destructive industrial operation along California’s coastline, pulling in approximately 2.5 billion gallons of seawater every day. In the process, it kills an estimated 1.5 billion marine organisms annually and affects roughly 46 miles of coastline and 93 square miles of ocean habitat. It also discharges massive volumes of heated water back into the marine environment, altering ecosystems and placing additional stress on already vulnerable species, including sea otters and leatherback sea turtles. This is precisely the type of harm the Clean Water Act was enacted to address.

In 2010, California adopted a policy to enforce the Clean Water Act’s requirements, mandating that facilities like Diablo Canyon reduce their ocean water intake by about 93 percent by 2024. That process, however, was never completed.

In 2016, regulators paused their analysis after PG&E announced plans to retire the plant. For years, that planned shutdown served as a stand-in for compliance. Decommissioning became the assumed solution, and PG&E reinforced that expectation through planning efforts and public commitments pointing to a 2025 closure.

But that expectation did not hold. In 2022, California enacted Senate Bill 846, extending Diablo Canyon’s operations to at least 2030, but likely much longer. Instead of requiring installation of technology to reduce environmental harm, the law allowed the plant to continue operating while paying mitigation fees in conflict with federal law.

At the same time, decommissioning efforts slowed significantly. Planning timelines became uncertain, key activities were paused, and PG&E began describing the shutdown schedule as “accordion-like”—expandable or contractable depending on future conditions. What had once been presented as an imminent retirement became something far less certain.

Allowing Diablo Canyon to operate without installing required technology effectively turns the Clean Water Act on its head. Instead of preventing harm, it permits ongoing ecological damage, defers compliance based on uncertain timelines, and substitutes mitigation payments for real, technology-based solutions.

The legal challenge to the permit argues that the Central Coast Regional Water Board violated the Clean Water Act by replacing a clear technology requirement with mitigation and speculation about future shutdowns. It also contends that agencies relied on outdated assumptions without reevaluating changed circumstances, particularly the extension of the plant’s operating life.

The challenge further asserts that there is no evidence showing compliance is infeasible and that SB 846 conflicts with federal law by allowing mitigation in place of required technology. At its core, the case asks whether regulators can indefinitely postpone compliance by pointing to a moving target.

This case is not just about a single facility. If regulators can treat future decommissioning as compliance, it creates a pathway for other plants to avoid installing environmental protections altogether—so long as they promise to shut down eventually.

That outcome would significantly weaken one of the central protections of the Clean Water Act. The Clean Water Act does not say “minimize harm someday.” It says: minimize harm now.