On the day that Exelon Corp. officially announced the closing of the Oyster Creek nuclear power plant in New Jersey, state officials unveiled a sweeping plan to revitalize Barnegat Bay, the ailing coastal waterway that provides the plant's cooling water and has borne the brunt of its effects.

The closure of the nation's oldest operating nuclear plant, which is to happen by the end of 2019, is neither the first - nor likely the last - among the nation's aging nuclear fleet. It raises the question of what will replace them.

Meanwhile, the 10-point plan proposed by Gov. Christie's administration is probably the most significant political attempt so far to address Barnegat Bay's decline, decades in the making.

Development in its watershed has increased erosion and runoff. And nutrients from fertilizer and other sources promote explosions of algae that smother the bay's underwater grasses, a nursery for finfish and shellfish.

The 10-point plan for the bay includes fertilizer restrictions, stormwater improvements, tighter water quality standards, open-space protections, and public education.

"After years of inaction and the bay's declining ecological health, we finally have a comprehensive plan that will prevent further degradation of the bay and begin the restoration," Christie said in announcing the plan.

Bob Martin, commissioner of the state Department of Environmental Protection, said dealing with Oyster Creek and restoring Barnegat Bay had been Christie campaign promises.

Oyster Creek's huge water intakes - used for cooling - trap and kill millions of fish and other organisms a year.

The Corzine administration had required the plant to build cooling towers, which would need less water. No date had been set.

Supporters of the project said those would cost $200 million, but Exelon pegged the cost at $800 million, far more than the plant's value.

Now, although the plant had been relicensed by the Nuclear Regulatory Commission to operate until 2029, it will close by Dec. 31, 2019. Martin said the company signed an administrative consent order that includes penalties if the plant does not close.

The plant employs 700 people, and can produce 630 megawatts of power, enough for 600,000 homes.

But it is far smaller than Jersey's other nuclear plants. It also has been dealing with a leak of tritium, a radioactive form of hydrogen that is a byproduct of reactors' making electricity.

"The plant faces a unique set of economic conditions and changing environmental regulations that made ending operations in 2019 the best option," Exelon chief operating officer Chris Crane said in announcing the closure.

In an interview Thursday, he said the plant was "small and uniquely troubled." Because of its age and design, it "has the same staffing and the same cost profile of a plant that could be twice its size."

Crane said the plant would continue to operate normally over the next nine years. "We don't plan on having a significant reduction in capital expenditures or maintenance expenditures. We intend to maintain it at the highest levels."

Once the plant is shut down in 2019, it will go into a regulatory status called "safe store," Crane said. The fuel will cool for 10 years in the reactor pool. Any time up to 50 years after that, decommissioning would begin, he said.

"It would depend on wherever the spent fuel is going at that time and whatever regulatory issues are prevalent at the time," he said.

The U.S. government has agreed to accept wastes from nuclear plants, and companies have paid into a fund to finance it, but no agreement has been reached on how or where that will happen. A plan to store waste in Nevada's Yucca Mountain has been nixed.

Crane said the company had established a $700 million fund for the decomissioning, as required.

He said there were no immediate plans to replace it. But he predicted that natural gas would become more prevalent among power plants.

Martin said the state would begin looking for new generation immediately. The plant provides 9 percent of New Jersey's electricity.

Some environmental groups called the closing of Oyster Creek the biggest piece of the overall package.

"It vindicates what we've been saying all along" about lax safety measures, said Dave Pringle, campaign director of the New Jersey Environmental Federation. "We would like it shut down sooner, but New Jersey was handed a lousy deal. Gov. Christie has played the hand as well as could be expected."

Given a relicensing appeal and other measures, "I think we're going to get less than nine years," he said.

Michael J. Kennish, a marine scientist at Rutgers University who has studied Barnegat Bay for more than 40 years and pushed for measures to save it, was cautiously optimistic.

Letting the plant run will cause nine more years "of mortality" among aquatic life, he said. But the measures to restore the bay, if officials follow through, will tip the balance in favor of recovery.

The plan is "a good initial step, something that should have been done earlier," Kennish said. "It supports a research agenda and monitoring. It also has a strong education component, which is very definitely needed."

But, he said, two big questions remain: "Is there enforcement? And where is the money coming from? Without those, it's sort of like reaching for the stars."

Martin said the state has $400 million in "Green Acres" funds, some of which could be directed to the basin.

The DEP also has committed $100 million during the next 10 years for grants and low-cost loans for stormwater improvement projects.

Most of the bay's watershed is in Ocean County, and officials there had balked at stormwater requirements, saying they were an unfunded mandate.

Even with the best plan, the bay will take decades to recover, Kennish said: "There is no quick fix to this."

William deCamp Jr., chairman of the advocacy group Save Barnegat Bay, said that while the plan has positive elements, it did not address the significant amount of nitrogen entering the bay from the air. Emitted by fossil-fuel burning to the west, it is blown east and often is carried to earth by rain.

He said the plan failed to address zoning and regulatory changes to curb development.

He also noted the lack of "any indication as to how our state's various bureaucracies will this time . . . accomplish what they have failed repeatedly to accomplish for over a generation. We note an absence of time lines."