* Young crabs at two-decade high, rockfish stable
* Oysters at 1 pct historic levels, water clarity poor
* Chesapeake home to 3,600 species, watershed covers 6 states
By Ian Simpson
WASHINGTON, Jan 31 The Chesapeake Bay, North America's biggest estuary, is still ailing but making some progress as it struggles to recover from over-fishing and pollution, a partnership overseeing its revival said on Thursday.
The number of juvenile crabs is the highest in two decades, rockfish are stable and last year's "dead zone," the part of the bay without enough oxygen to support life, seems to be the smallest since 1985, the Chesapeake Bay Program said in its 2011-12 "Bay Barometer."
On the down side, water clarity was very poor and only a third of the bay met standards for dissolved oxygen, a measure of water's health. The oyster population also was at less than 1 percent of historic levels.
"While we clearly have a lot of work to do, the bay is resilient and we have reason for hope," Nick DiPasquale, director of the federal and state program, said in a statement.
The Chesapeake Bay, home to more than 3,600 species of plants and animals, has been fouled by decades of over-fishing and pollution. Pollutants include sediment, manure, trash and chemicals that flow into it from its 64,000-square-mile (166,000-square-km) watershed across six states.
The Chesapeake Bay Program was formed in 1983 to restore the estuary, where salt water from the ocean mixes with fresh water. It includes Maryland, Pennsylvania, Virginia, the District of Columbia, the Environmental Protection Agency and citizens groups.
The group said that most of the bay's feeder freshwater streams were in poor or very poor condition. Water murkiness and algae levels in 2011 were the worst since 2009.
But the big Susquehanna Flats grass bed survived Tropical Storm Lee in 2011. In another sign of health, grasses in the middle of the Chesapeake showed "dramatic increases," the program said.
The adult female crab population was still within the sustainable range in 2012 despite falling for two years.
Nitrogen and phosphorus, components in fertilizers that contribute to algae growth, each moved about 20 percent closer to their targets from July 2009 to June 2011 under a bay "pollution diet."
Sediment was about 30 percent nearer its target, helped by more forested buffers being planted to limit runoff into streams and rivers.
In a separate report, the U.S. Geological Survey said this month that nutrient and sediment trends at nine bay monitoring sites had shown an overall lack of improvement through 2010. (Reporting by Ian Simpson; Editing by Leslie Adler)