ON THE CHESAPEAKE BAY - Motoring through lifeless waters, charter boat captain Richie Gaines suddenly ran into a patch boiling with hundreds of silver-bellied rockfish, packed together so tightly they were leaping out of the water.
Tails thrashed. Seagulls shrieked and dove at the feast near the mouth of the Chester River. Gaines unholstered his fly rod, plucking out 27 fish in just a few minutes, reeling in another with nearly every cast.
He might have been delighted - but instead he found the thicket of fish disturbing. This summer has been one of the worst in the Chesapeake Bay's history for low-oxygen "dead zones," which force fish to flee into the few remaining areas where they can breathe.
"We call it `the squeeze,'" said Gaines, president of the Chesapeake Guides Association. "Eighty percent of the fish get squeezed into 20 percent of the water. Getting them is like shooting fish in a barrel. That's good for fishermen, but the bad news is that all the charter boats are annihilating them. It's a sign that the bay is dying."
These dead zones occur when farm fertilizer and other pollutants mix with warm water to feed algae blooms, which rot and consume oxygen, making it hard for marine life to breathe. The wind blows this bad water around the bay, and fish and crabs move into the few remaining high-oxygen areas. Oysters can't escape, so they often die.
"People tend to think of the dead zone in real stark terms, that it kills everything in it," said Bill Goldsborough, senior fisheries scientist with the Chesapeake Bay Foundation. "But it's actually a very subtle thing. Of course, fish can move, and you see lots of fish and crabs being herded and crowded by the moving dead zone. Fishermen can have a phenomenal day if they hit it just right."
Early last month, about 41 percent of the bay's main section had less than the 5 milligrams of dissolved oxygen per liter of water needed for healthy fish reproduction, the second-worst August reading in two decades of monitoring, according to the federal Chesapeake Bay Program. By late last month, as the waters cooled, the number was 28 percent.
David Jasinski, water-quality data analyst for the University of Maryland Center for Environmental Science, said water with slightly less than 5 milligrams of oxygen wouldn't immediately kill a rockfish or crab. But it would stress their health, retard their growth, harm reproduction and force them to keep moving in search of good water.
Most of the lowest-oxygen areas in the bay are toward the bottom, where the heavier, saltier water settles, Jasinski said. The lighter fresh water tends to rise to the top, where it absorbs more oxygen. Salt water and fresh water don't like to mix. Between these layers is an invisible barrier to circulation and oxygen exchange, he said.
During July and August, the top layer of water gets so hot - sometimes approaching 90 degrees - that fish can't tolerate it and plunge toward cooler depths. But they hit the invisible wall at about 20 feet and discover that the saltier water beneath has too little oxygen, Jasinski said.
So they cluster right around this barrier, he said.
"They get squeezed from the bottom, because there's low oxygen or no oxygen down there," Jasinski said. "And they get squeezed from the top, because it's too warm for them up there."
Complicating this trend is the wind. It can bend the invisible barrier as breezes blow top water to one side of the bay or the other. Winds from the west sometimes slosh most of the higher-oxygen surface water to the east side of the bay, and that forces the colder, saltier, oxygen-starved water to the west, Jasinski said.
When this happens, thousands of crabs on the west side of the bay flee, stampeding up the beaches of Calvert County. "It isn't a good thing with these crabs basically running away from water they can't breathe in," Jasinski said. "They'll climb up on pilings or rocks - whatever they can - to breathe."
During a recent fishing trip off of Kent Island, Gaines, 47, talked about his life on the bay and how it has changed as pollution levels have risen and oxygen levels have dropped. He is the son of a Southern Maryland marina owner and has worked as a fishing guide for the past 18 years.
As he roared along in his 25-foot-long motor boat, the afternoon sun blazed over heaped storm clouds, casting a copper glow onto the lead-gray waves. Off Love Point, he slowed and pointed at a reddish-brown stain in the water. It was an algae bloom.
"Here's a little bit of funky water here," Gaines said. "We've seen an awful lot of these algae blooms this summer."
Over the decades, fish that feed in deeper waters, such as flounder and sea trout, have become more scarce in the bay. Underwater grasses as well as oyster and crab populations have fallen off, as has the fishing industry.