California’s reservoirs are releasing methane into the atmosphere, and the state has no system in place to measure how much. That gap is now drawing scrutiny from environmental groups who want regulators to fix it.

A coalition of advocacy organizations filed a push with the California Air Resources Board to require mandatory methane tracking at major water storage facilities statewide. The LA Times broke the story on April 15, 2026, detailing how the coalition argues that California can’t meet its climate commitments without accounting for emissions from an overlooked source sitting in plain sight.

Here’s the basic chemistry. Organic material, dead leaves, algae, sediment, plant matter, sinks to reservoir floors and breaks down in low-oxygen conditions. That anaerobic decomposition produces methane, which rises through the water column and vents into the air. Nobody disputes the mechanism. The dispute is over whether anyone’s responsible for counting it.

Right now, nobody is.

California operates some of the largest reservoirs in the American West. Shasta Lake, Lake Oroville, and Folsom Lake alone hold staggering volumes of water, and the California Department of Water Resources monitors them constantly for water quality, flood risk, and delivery schedules. But methane emissions don’t fall neatly into that mandate, and air quality regulators haven’t filled the gap. The result is a blank ledger at a moment when the state says it’s serious about tracking every ton of greenhouse gas it produces.

The stakes aren’t trivial. Methane is roughly 80 times more potent as a warming agent than carbon dioxide across a 20-year period, according to the Environmental Defense Fund. Even sources that look small on paper can carry real weight when you’re chasing aggressive emissions targets. California has committed to carbon neutrality by 2045, and that’s a deadline that doesn’t leave room for uncounted sectors.

“We’re asking the state to apply the same rigor to reservoir emissions that it applies to oil fields or landfills,” one coalition member told reporters in April.

The science connecting reservoirs and methane isn’t new. A 2016 study in the journal BioScience estimated that reservoirs globally could account for roughly 1.3 percent of worldwide greenhouse gas emissions. That figure caught researchers off guard when it first circulated, though it’s become more familiar since. Tropical reservoirs tend to emit at higher rates because of heat and abundant vegetation, but temperate systems like those California relies on still produce meaningful quantities, particularly during summer months when stratification is strongest.

Warmer temperatures are making conditions worse. As California’s climate heats up, the thermal layering inside reservoirs intensifies. Warmer water floats on the surface, cooler water sinks, and that stratification traps organic material at depth in exactly the kind of oxygen-starved environment where methane production accelerates. The state’s reservoirs have also seen elevated algae blooms over the past several summers, and decomposing algae is itself a significant methane source.

Part of the accountability problem is structural. Water agencies and air quality regulators don’t share jurisdiction over reservoir surfaces, and historically they haven’t coordinated closely. The California Air Resources Board tracks emissions from refineries, power plants, agriculture, and landfills. Reservoirs sit in an awkward middle space, managed by water agencies whose statutory mission doesn’t include greenhouse gas accounting. Environmental groups argue that gap was tolerable when reservoir methane seemed like a rounding error. It’s harder to justify in 2026, when the state is trying to squeeze emissions reductions out of every available source.

The coalition isn’t asking for anything exotic. It wants systematic monitoring protocols at major facilities, baseline data collection, and eventually reporting requirements that feed into California’s greenhouse gas inventory. Whether the Air Resources Board moves on it is a different question.

Even if monitoring starts today, building a reliable emissions profile takes years. Researchers studying reservoir methane globally have found that emissions vary widely depending on water temperature, depth, organic load, and seasonal cycles. Getting accurate numbers out of Shasta Lake or Folsom Lake would require sustained measurement, not a one-time survey.

California has 2045 as its carbon neutrality target. That’s 19 years from now, which sounds like time. It isn’t.