ANNAPOLIS, Md. -- Billions of dollars have been spent to restore the polluted Chesapeake Bay since the rallying cry "Save The Bay" was plastered on a popular blue-and-white bumper sticker 30 years ago.

But for the scientists and activists working to revive the nation's largest estuary, it's clear the bay has not been saved. Conservationists say the job is more difficult than they imagined, and they're battling fatigue.

The Chesapeake teemed with oysters and blue crabs when European settlers arrived but is now plagued by algae blooms and fish kills. Oysters are nearly wiped out. Miles-long swaths of the bay are called "dead zones" because summertime oxygen levels are too low to support most life.

When the governors of Maryland, Virginia and Pennsylvania met recently in Annapolis and announced they wouldn't meet the cleanup goals that had been set for 2010, conservationist Will Baker wrote them a letter expressing his frustration.

"What the bay needs now is your leadership to get the job done," wrote Baker, president of the not-for-profit Chesapeake Bay Foundation. "It does not need more public signings of directives. It does not need more photo ops."

Conservationists agree that the six states with streams flowing into the Chesapeake have made great strides in improving water quality. Maryland and Virginia have set aside hundreds of millions to upgrade sewage treatment plants. Pennsylvania planted more than 600 miles of forest buffers along waterways last year. Farmers in the region get paid to plant winter cover crops and take other steps to reduce excess fertilizer from entering the water. Maryland even requires lower-phosphorus laundry detergent.

Despite the improvements, the bay foundation has given the bay a "D" grade for the ninth consecutive year.

"For the first 15 years, we truly believed the Chesapeake Bay could be saved. But with the population growth in the area, as fast as we took two strides forward, we would take three strides back," said Ann Swanson, who heads the Chesapeake Bay Commission, which works with lawmaking bodies in the states around the bay.

Environmentalists worked to stop pollution going into the bay from factories or sewage treatment plants. But the bay is choked with pollution from the 16.7 million residents of the watershed of nearly 14,700 square miles. The population in the area has more than doubled since 1950.

"The rate of population growth, the number of people moving into the watershed, it's gotten to the point we can't ignore it anymore," said Jeff Corbin, assistant secretary for Virginia's Office of the Secretary of Natural Resources.

Working to restore the Chesapeake is somewhat like fighting hunger or poverty, Baker said. The aim is noble, and progress can be made, but the job will never be done.

"I don't think that on this planet we're ever going to get there in terms of fixing the environment," he said.

But he and other conservationists say it is possible to revive the Chesapeake -- perhaps restoring it to the kind of bay seen in black-and-white photos of men standing next to chest-high mounds of oysters, when parts of the bay were so thick with underwater grasses that some boats couldn't safely navigate them.

Scientists say there needs to be a tougher resolve for states to reduce nitrogen and phosphorus pollution. That could mean pouring millions into helping farmers reduce pollution, requiring cleaner cars that don't emit so much nitrogen or restricting development.

The bay won't be saved, or even improved, without a bigger push to change behaviors that put pollutants in the Chesapeake, conservationists say.

"It's a national treasure, and we're at a major crossroads in the bay," Swanson said. "Do we want to preserve it, or do we choose to let it go?"