More than 200,000 fish have died in Maryland waterways in the past five days in a drought-induced fish kill that appears to be one of the worst in more than a decade, the state Department of Natural Resources reported yesterday.

Most of the deaths have occurred in the tributaries of the Magothy River in Anne Arundel County and the Patapsco River, which flows through Howard County to Baltimore's Inner Harbor.

But state officials said they are beginning to hear reports of large kills along the Severn River in Anne Arundel and on the Eastern Shore. Most of the dead fish are minnows, but the fish kills also have claimed eel, yellow and white perch, largemouth bass and catfish.

State officials said the likely cause of the deaths is a drought that is aiding the spread of algae, thereby robbing waterways of oxygen. If the drought continues through July, as is expected, as many as 1 million fish could die, state officials said.

"We expect the fish kill to continue until we get a long, cold weather snap in addition to significant rain," said Charles A. Poukish, an environmental specialist with the Maryland Department of the Environment. "It's going to take more than just one severe rainstorm."

The period between June 1998 and May 1999 was the second-driest 12-month stretch on record in Maryland. The National Weather Service classifies it as an "extreme drought." If a region has 15 percent less rainfall than normal, it has crossed the line into drought. Rainfall across Maryland is 30 percent below normal.

The heat and lack of rainfall have resulted in warmer than average water temperatures in many Maryland rivers, particularly in the shallow creeks, coves and small tributaries that cover the Chesapeake Bay area. Warmer water means more algae. More algae mean less oxygen in the water for fish to breathe through their gills.

Virginia, by contrast, has not experienced widespread fish kills this year despite unseasonably low river levels. John Kauffman, regional fisheries manager with the Virginia Department of Game and Inland Fisheries, said that rivers running through Northern and Central Virginia tend to flow from the mountains and are aerated as they flow downhill, reducing the possibility of oxygen depletion.

The typical oxygen level in the water is five to eight parts per million, the unit biologists use to measure water conditions. Below five parts per million, fish start to struggle with breathing. Below two parts per million, the water is hypoxic, when fish kills can occur.

In many parts of the Patapsco and Magothy, the oxygen level is hovering between 0.5 and 0.7 parts per million at night, when algae oxygen consumption is at its peak.

"The last time we experienced such a broad oxygen crash was in the mid-1980s," Poukish said.

Many residents were concerned that what they were seeing was a repeat of 1997's devastating Pfiesteria piscicida outbreak, which killed thousands of fish and sickened some bay area residents. State scientists said yesterday that the toxic microbe is not responsible.

"These fish do not have lesions or any other type of anomaly" symptomatic of pfiesteria, Poukish said.

The fish kills pose little threat to humans. The vast majority of those dying are small, minnow-type fish not eaten by people. State health officials warned those removing the dead fish from the water or waterside to use gloves, as the carcasses are breeding grounds of all sorts of microorganisms, some harmful. Swimming in fish kill areas should also be avoided, they said.

The overall Chesapeake Bay fish population should not be affected either, even if the death toll in tributaries tops 1 million, state officials said.

As water loses oxygen, fish move closer to the surface, where oxygen is slightly more plentiful. Boaters who peer into the brown, algae-infested waters around the Magothy can see the clearly distressed fish, barely moving, their lips just kissing the surface.

The sight particularly troubles some watermen and scientists who work on the bay.

"Oh, isn't that a shame. They are so obviously in trouble," said Mike Naylor, an environmental specialist with the Department of Natural Resources, as he pointed to a struggling yellow perch. "It's easy prey for ospreys and sea gulls, if it doesn't die first."

Staff writer Jennifer Lenhart contributed to his story.