Upholding a lower court decision, the 9th U.S. Circuit Court of Appeals ruled Thursday that a Lahaina sewage treatment plant is violating the U.S. Clean Water Act by allowing wastewater to reach the ocean.

The unanimous ruling by a three-judge panel is a victory for Maui community groups that for at least a decade have been battling to protect coral reefs and users of Kahekili Beach Park from pollution.

“At some point the county has got to stop fighting this, because no one believes them anymore,” said Earthjustice staff attorney David Henkin, who represents the Hawai‘i Wildlife Fund, Sierra Club-Maui Group, Surfrider Foundation and West Maui Preservation Association.

The county issued a statement Thursday, saying, “The court fashioned a new theory of liability, where any small fraction of pollutants that can be fairly traceable to a source triggers liability.

“In creating this new theory, the court rejected both the U.S. Environmental Protection Agency’s opinion as well as the plain text of the Clean Water Act itself. The county is reviewing the order,” the statement said.

The county, which has been defending itself in court since 2012, argued that Clean Water Act permits were not necessary because pollutants are discharged from injection wells a half-mile from the ocean and flow into the ocean only indirectly in groundwater.

What’s more, county attorneys argued that the treatment plant isn’t the only source of pollution contributing to impaired coastal waters.

But the appellate court wasn’t buying the argument.

“At bottom, this case is about preventing the county from doing indirectly that which it cannot do directly,” the court said in its opinion.

The court noted that the county could not build an ocean outfall to dump pollutants directly into the ocean without a Clean Water Act permit.

“It cannot do so indirectly either to avoid CWA (Clean Water Act) liability. To hold otherwise would make a mockery of the CWA’s prohibitions,” the opinion said.

The Lahaina Wastewater Reclamation Facility, which serves West Maui, injects 3 million to 5 million gallons of treated sewage into the ground each day.

In 2011 an EPA-funded study used tracer dye to link Lahaina sewage to nearshore waters off Kahe­kili Beach. In November a U.S. Geological Survey study found that discharge from the sewage treatment plant has been drastically undermining the coral reefs off Kahekili for years.

Henkin called Thursday’s ruling a victory for Kahekili Beach users and for anyone who cares about protecting the ocean or any other waterway.

“No more can the County of Maui or other polluters attempt to circumvent the Clean Water Act by using groundwater as a sewer to carry pollution into the ocean or water bodies,” he said.

“If they asked me, I would strongly advise the county to stop spending millions on lawyers and start fixing the problem,” Henkin said.

In an earlier settlement, the county agreed to pay a $100,000 fine and spend $2.5 million for infrastructure designed to reuse the wastewater if the courts upheld the case’s 2014 U.S. District Court ruling.

While county officials weigh their legal options, the county Department of Environmental Management will continue to aggressively pursue recycled water reuse as a primary goal, according to Maui County.

“These projects are not inexpensive to install and to operate — the energy costs of pumping water from place to place are very high and are dependent upon council’s appropriation of sufficient budget,” a news release said.

Even so, reuse projects are being planned in all parts of the county, including in Lahaina.

“We are working on an alternative disposal method instead of using the injection wells as the primary source of disposal,” the release said of the Lahaina proposal. “This alternative utilizes an existing reservoir located at the 800 foot elevation, and plans are to utilize existing pipeline infrastructure to pump the water up to this reservoir and utilize the excess recycled water for irrigation.”