The Massachusetts Supreme Judicial Court ruled Tuesday that the state process used to approve a development plan along Boston's waterfront was illegal. The unanimous decision scuttles a plan covering 42 acres of prime Boston waterfront and gives the city a chance to start a new process.

"We're thrilled," said Deanna Moran of the Conservation Law Foundation, which filed the lawsuit. "We've been saying for years that the state's municipal harbor planning process is fundamentally flawed. And today we got the news that we were hoping for, that the court agrees."

What the SJC agreed with was CLF's contention that the state's politically appointed Secretary of Energy and Environmental Affairs did not have the legal authority to approve the city's initial waterfront development plan. Instead, the court ruled that that authority rests solely with the state's Department of Environmental Protection. While DEP falls under the jurisdiction of the EEA secretary, the SJC ruled that approval had to come from the professional regulators working in the DEP.

The DEP is rightfully in charge of licensing projects under Chapter 91, the Massachusetts Public Waterfront Act, which regulates development along waterways, Moran said.

"They are the ones who are dealing with developers and other project proponents, day in and day out," she said. "They know that statute and those regulations like the back of their hand, and they are the ones who should be making the decisions about when it's okay — if it's ever okay — for a developer to depart from those rules."

The plan that was approved by EEA Secretary Matthew Beaton in 2018 had allowed developers to skirt state regulations about the size of developments, Moran said.

"We have seen a trend over the past 10 years or so where the municipal harbor planning process has been used to allow developers to very significantly depart from Chapter 91 rules, on things like height and lot coverage," she said. "We've also seen a pretty disturbing trend where instead of making trade-offs for departing from those rules by providing other benefits to the public on site, developers have kind of proposed to just monetize that departure. And it's become a pay to play system."

Those in the state's real estate development community see things differently.

"This is not something that was done in the dark of night," Tamara Small, CEO of the commercial real estate development association NAIOP Massachusetts, said of the harbor plan. "This is something that had hundreds of public hearings, extensive public input over the course of many, many years. And most importantly, it did include quite a bit on climate resiliency."

NAIOP Massachusetts filed an amicus brief in the case, supporting the EEA secretary's right to approve municipal harbor plans.

Small said the SJC's ruling will be felt beyond the city limits of Boston.

"I think every community that has a municipal harbor plan is deeply concerned about this decision," she said.

Small said that NAIOP Massachusetts is hearing from members concerned both about future projects and those approved in the past.

"If they were signed off by EEA and not by DEP, what does that mean, if this is the court's view?" she asked. "I think without a doubt that really creates some uncertainty there, and that's something that needs to be addressed ASAP."

Moran of CLF says past approvals shouldn't be a concern, pointing to a footnote in Tuesday's ruling that notes "the time to challenge the department's licensing decisions is finite."

"So this is really a forward-looking decision, which is what CLF wanted," Moran said. "We never intended to try and go back in time and upset any of those previously approved projects. You know, many of them are built. It's done. We want this to impact the downtown municipal harbor plan and municipal harbor plans going forward."

The SJC ruling essentially throws out the harbor development plan introduced under then-mayor Marty Walsh, and now hands that opportunity to Mayor Michelle Wu. The DEP did not immediately respond to a request for comment.

While campaigning for mayor last fall, Wu came out against the city's municipal harbor plan.

Wu's office did not immediately respond to a request for comment from GBH News about the ruling, but in a statement last September, she said, "Boston has the right to hold a community planning process for a waterfront that is accessible, resilient, and equitable."