It looks like the ongoing legal battle over pollution from Maui County’s sewage treatment plant in Lahaina will culminate in a high-profile skirmish at the U.S. Supreme Court.

The nation’s highest court agreed Tuesday to hear the case, which is likely to have far-reaching implications as it addresses the scope of the federal Clean Water Act.

The 9th U.S. Circuit Court of Appeals ruled last year that the county has been in violation of federal law since the Lahaina Wastewater Reclamation Facility opened in the early 1980s, a decision Maui County appealed to the Supreme Court.

The Lahaina plant disposes of 3 million to 5 million gallons of treated sewage daily via underground injection wells. Environmentalists have argued for decades that pollution from the wells is contaminating groundwater that seeps into the ocean, killing coral and triggering algae blooms in West Maui waters.

When an Environmental Protection Agency-funded study in 2011 used tracer dye to link the Lahaina sewage to nearshore waters off Kahekili Beach, four Maui groups — the Hawai‘i Wildlife Fund, the Sierra Club Maui Group, the Surfrider Foundation and the West Maui Preservation Association — sued, accusing the county of violating the Clean Water Act.

In 2015 the county agreed in a conditional settlement to spend $2.5 million on projects to divert treated wastewater from the Lahaina facility and pay a $100,000 penalty to the federal government. The settlement remains conditional as long as the county is appealing the case.

In 2017 a U.S. Geological Survey study concluded that discharge from the sewage treatment plant was drastically undermining the coral reefs off Kahekili.

“The county shouldn’t be allowed to use the groundwater as a sewer,” said David Henkin, the Earth­justice attorney representing the groups.

The county, however, continued to appeal the case, insisting the plant’s injection wells are a safe and scientifically sound method of disposing treated recycled water.

“The truth is that the coral on the west side is generally in healthy condition, with sites, including Kahekili, being called ‘pristine,’” the county said in a statement last week.

The Supreme Court’s decision to grant Maui County’s petition means “there’s hope the county won’t be forced, ultimately, to develop offshore sewage outfalls,” the release said.

“We all want unpolluted waters, healthy coral and fish. But we want workable solutions, not onerous and costly government red tape,” county spokesman Brian Perry said in the release. “This is a home-rule issue that should be addressed here, not by far-off regulators imposing rules that don’t properly address our real-world problems.”

Perry added that if the lower court’s decision is allowed to stand, thousands of residents and businesses may be required to get federal permits for recycled water irrigation systems, cesspools and septic systems.

The Maui County Council has authorized paying its private attorneys more than $4 million to litigate the case.

Meanwhile, the appeal has drawn nationwide attention. More than a dozen states, the Trump administration and other groups, including the National League of Cities and the National Association of Counties, have urged the high court to review the case.

The landmark 1972 Clean Water Act imposes restrictions on pollution that enters lakes, rivers, streams, oceans and other navigable waters. It is illegal, for example, to dump pollution from a “point source,” such as a pipe, into such waters without a permit.

The law is less clear when a pollutant comes from groundwater, a streambed or marsh.

In fact, two other appellate courts ruled on the question in 2018, interpreting the law in opposite ways. It was that split that helped pave the way for the Supreme Court to take up the case.

The outcome could affect permitting for pipelines, ash ponds and other disposal sites and may have implications for a variety of operations, including farms and coal mines.

“Maui County now becomes the poster child for every polluting industry of the United States,” Henkin said.

“It’s a huge, tragic waste, both for the taxpayer money and for the increasing danger to our reefs,” said Hannah Bernard, president of the Hawai‘i Wildlife Fund.

The court’s decision to hear the case comes as the Trump administration separately is proposing to roll back Clean Water Act protections for wetlands and waterways.