A federal judge ruled Tuesday that Maryland’s environmental review of a light-rail Purple Line had sufficiently considered potential impacts on the Kenk’s amphipod, which is a candidate for federal endangered-species listing.

A federal judge on Tuesday dismissed most of a lawsuit seeking to block construction of a light-rail Purple Line in Maryland, saying the project’s environmental review did not violate federal protections on endangered species and migratory birds.

The ruling allowed the Maryland Attorney General’s Office to almost immediately appeal the one issue remaining from the lawsuit — a court-ordered redo of the Purple Line’s ridership projections to account for Metro’s decline — that blocks the state’s access to $900 million in federal construction grants.

The state filed an appeal later Tuesday to the U.S. Court of Appeals for the D.C. Circuit. The court filing did not include any details, but the appeal is expected to focus on the court-ordered ridership analysis. Plaintiffs in the lawsuit have argued that the state’s previous study presumed a “robust” Metro system that has since declined. State and federal officials have said a subsequent analysis found that Metro’s declining ridership, even if it continued, wouldn’t have a significant impact on the Purple Line.

The Purple Line would be operated separately from Metro, but about a quarter of the light-rail line’s passengers are expected to transfer to and from the subway system.

A spokesman for the Justice Department declined to comment on the latest ruling.

It’s unclear what impact Tuesday’s decision or the appeal will have on the Maryland Department of Transportation’s previous statements that it would run out of money to continue the project’s pre-construction work as of June 1. Maryland Transportation Secretary Pete K. Rahn said in a court filing that due to limited state funds, the state would have to suspend design and engineering work on or shortly after June 1 unless the state had a “foreseeable path” toward resolving the lawsuit and clinching federal aid.

Rahn declined to address the June 1 deadline Tuesday, saying in a written statement, “This project will provide tremendous value and benefits to the surrounding communities and the state, and we are hoping the appellate court will move forward expeditiously.”

Maryland officials have said the state could begin building the $2 billion light-rail line between Montgomery and Prince George’s counties within a few weeks of securing federal funding, and the Trump administration recently said it will continue to consider the project for federal aid while the lawsuit is pending. Congress has appropriated $325 million toward the Purple Line, but Maryland officials can’t access that money until a court reinstates the project’s federal environmental approval, which U.S. District Judge Richard J. Leon revoked in August when he ordered the ridership update.

In his final decision Tuesday, Leon let his previous ruling on the ridership issue stand. However, he said he agreed with the government that the Purple Line’s federally approved environmental review had sufficiently considered potential impacts on any endangered species and migratory birds. Leon did not explain his decision, saying he would do so “in the near future.”

John M. Fitzgerald, an environmental lawyer and a plaintiff in the 2014 lawsuit, said the plaintiffs want to hear the judge’s reasoning. Asked whether they plan to appeal, Fitzgerald said, “We’re certainly reviewing all of our options.”

Fitzgerald and other Purple Line opponents had argued that the state’s environmental study didn’t sufficiently consider harm that the line’s construction could cause to two rare, tiny crustaceans found near and downstream from the line’s planned alignment. One of the shrimplike creatures, the Hay’s Spring amphipod, has been listed as a federally protected species since 1982, and the Kenk’s amphipod is being considered for federal endangered-species listing.

The Purple Line’s environmental impact study also didn’t consider ways to avoid or minimize impacts on federally protected migratory birds, the plaintiffs said. The Purple Line’s construction, they said in a court filing, “will likely lead to many [migratory bird] deaths” and cause other harm.

Maryland transit officials have said state and federal studies did not turn up any endangered species along the planned rail alignment. State officials have said that a study did find Kenk’s amphipods in a spring but that it was too far from the Purple Line alignment to be harmed.

Protections on migratory bird nests prohibit any Purple Line crews from cutting trees in “forested” areas during the nesting season, from April to September.

Leon had been under pressure to issue a final ruling in the case since mid-May, when the Maryland Attorney General’s Office asked a federal appellate court to require him to decide the entire lawsuit so the state could appeal the ridership issue. The state has said legal delays have cost more than $13 million a month and could jeopardize a $5.6 billion, 36-year public-private partnership on the project.

Greg Sanders, of the Purple Line Now advocacy group, said Leon’s final ruling offers a “path forward” on the project — either an appeal or an update of the ridership forecasts — that he believes should stave off any slowdown in pre-construction work.

“We’re now on dramatically firmer ground than we were even a few hours ago,” Sanders said after the ruling.