Island activists and local lawmakers say they will keep the pressure on Pilgrim Nuclear Power Station owners to decommission the aging boiling water reactor quickly and safely, following a decision to close the plant.

Entergy, the New Orleans-based corporation that owns and operates Pilgrim, announced Tuesday it will shut down operations at the nuclear plant in Plymouth. Falling wholesale energy prices, lower profits and increased operational costs are all factors in the decision. The plant is slated to close no later than June 1, 2019, and possibly as much as two years earlier.

Cong. William Keating, who represents the district that includes Martha’s Vineyard, welcomed the company’s decision but was harshly critical of its safety record.

“Entergy’s shutdown announcement was not surprising given their unwillingness to deal with current safety standards,” Mr. Keating said in a statement. “Great scrutiny is necessary to make sure Entergy is responsible for maintaining proper safety standards throughout the closure process, something they failed to do during their operations.”

Island activists who have lobbied for the closure said there would be little celebration, and that the news will not end their protest of nuclear energy.

“It was long overdue,” said Mas Kimball of Oak Bluffs, who helped organize opposition to the plant. “Now it’s just a matter of seeing how quickly it can be done and what Entergy is going to do in terms of decommissioning it properly. I don’t think the activism is going to end. We have to keep our eyes and ears open.”

Ann Rosenkranz of West Tisbury, also active in opposition to the nuclear facility, said the news was encouraging, but she was disappointed the plant would not be shut down sooner.

“Entergy’s main concern is their financial burden,” Ms. Rosenkranz said “That really is not where we’re coming from at all. We’re coming from a standpoint of our health, our livelihood, our environment. We are less than 50 miles from the plant. If we are downwind from any kind of radiological accident, we have no evacuation plan.”

She said even a relatively minor accident at the plant could leave the Island devastated by nuclear contamination.

“We really would lose the Island,” she said. “We would all be relocated and unable to return home.”

In an announcement that surprised many on Tuesday, Entergy said economic issues prompted the decision to close the plant. But the company conceded that a recent decision by the Nuclear Regulatory Commission (NRC) to rank the Plymouth facility among the nation’s least safe nuclear plants was also a factor.

Entergy officials projected it would cost at least $45 million to respond to NRC safety concerns, which were detailed following an inspection earlier this year. Even without safety improvements, the operation was losing money, the company said in a news release.

“Before considering any impairment or the decision to close the plant, Pilgrim was expected to incur annual after-tax net losses on an operational basis ranging from approximately $10 million to $30 million for 2015, 2016 and 2017,” the release said.

Sen. Edward Markey, long an opponent of the Pilgrim plant, said the closure refutes industry claims that nuclear energy is safe and inexpensive.

“Pilgrim Nuclear Power Station is just the latest example of how nuclear power simply cannot compete in the current energy market,” he said in a statement. “Alongside the economic conditions that Entergy blames this closure on, there also have been decades-long and repetitive operational safety and security concerns with the facility that have contributed to this announcement.”

Entergy is obligated by agreement with ISO New England, the nonprofit corporation that operates the power grid, to provide energy until 2019.

But the plant is scheduled for refueling in 2017, and company officials said it may make more sense to close the plant and begin decommissioning before that. A final decision on the closing date is expected in the first half of 2016.

A decision to close the plant earlier will depend on whether other sources of electricity can be found.

In a statement, Gov. Charlie Baker expressed concern that the loss of power generated at Pilgrim could trigger an energy shortage.

Entergy says it produces enough electricity to power approximately 600,000 homes, about 14 per cent of the energy produced in Massachusetts.

Cape and Islands Rep. Timothy Madden and Sen. Dan Wolf said attention should now turn to decommissioning the plant quickly and safely.

“There is a question about whether there are sufficient funds,” Mr. Madden told the Gazette by phone this week. “We’re going to do our due diligence to make sure the spent fuel rod [disposal] and decommissioning is done safely and done quickly.”

In a statement, Mr. Wolf concurred. “Now is not the time to relax,” he said.

Entergy says it has $870 million set aside for decommissioning.

Pilgrim Nuclear Power Station opened in 1972.

In 2012, the NRC renewed Entergy’s license to operate the plant through 2032.

According to Entergy, the plant employs 600 workers, and adds 900 temporary employees during refueling operations every two years.