And overall, bay grasses are falling far short of the goals for restoring the bay.

"The bay is getting warmer and dirtier, so the prognosis is not great," said Dr. Robert J. Orth, a scientist with the Virginia Institute of Marine Science who leads the annual bay grass survey. Institute scientists take aerial photos of the bay to document the grass beds.

In this area, survey results were mixed for 2007. Declines were documented in the Patapsco, Magothy, Chester and Severn rivers and in Eastern Bay.

The West and Rhode rivers once again continue to have no documented grass beds, while the South River had just 8 acres, up from none at all in 2006.

Part of the reason for the decline could be that only one species of grass - widgeon grass - lives in this area, so when the conditions aren't right for that one species, there can be a big difference. Also, like a weed, widgeon grass tends to disappear and reappear, Dr. Orth said.

"Sometimes it's there, sometimes it's not," he said. "It just comes and goes."

One of the reasons for declines in this area could be the drought of 2007. While droughts usually mean less pollution flowing into the water, they also mean higher salinity levels and often warmer temperatures.

That could have doomed the widgeon grass, which was suddenly forced to survive in a higher salinity environment.

The Severn River continues to have the greatest abundance of bay grasses in this area, nearly

326 acres last year, according to the report. The Magothy River also has significant grass beds - though the 83 acres last year was a big drop from more than 300 acres just two years ago.

Dr. Orth said scientists are stumped as to why the Magothy and Severn do well compared to the South. Development and pollution sources could be among the reasons for the difference, he said.

"We are intrigued by it and no one has a clear answer," Dr. Orth said.

Overall, bay grasses are suffering throughout the Chesapeake.

The Chesapeake Bay Program has a goal of bringing the bay's underwater grasses to 185,000 acres by 2010. In 2007, the total acreage of bay grasses was 65,000, which is just 35 percent of the goal.

The 2007 grass acreage was up 10 percent from 2006, but still fell short of the recent high of 90,000 acres in 2002.

Underwater grasses are a vital component of a healthy Chesapeake Bay, as they provide food for birds and a hiding spot for juvenile crabs, rockfish and other critters. They also help improve water clarity, put oxygen into the water and slow wave action along the shoreline.

"Underwater grass beds are one of the two dominant aquatic habitats in the bay, the other being oyster reefs," said Bill Goldsborough, a senior scientist with the nonprofit Chesapeake Bay Foundation. "These are critical habitats for a wide range of species."

But underwater grasses often suffer in the Chesapeake Bay. Harmful algae blooms and sediment pollution block light from reaching the grasses. Too much or too little rain can cause problems, too, as happened in 2007.

A die-off in eelgrass in 2005 in the southern bay is to blame for some of the ongoing woes with blue crabs, officials said. With no grasses in a vital nursery area, juvenile crabs had nowhere to hide from predators, so their numbers dropped.

As a result, crab reproduction was poor in 2006, and the harvest was one of the worst on record in 2007.

Now, officials in Maryland and Virginia are enacting crabbing restrictions to curb the harvest in hopes of bringing the population back.

To restore bay grasses, officials agree that major types of pollution - sediment that clouds the water, nutrients that fuel algae blooms - need to be reduced. And scientists are looking at why species succeed in different areas, and could adjust their planting efforts.