Officials with the Maryland Department of the Environment are investigating the fish kill, which claimed an entire school of young Atlantic menhaden that became trapped in the oxygen-deprived water south of Annapolis. It's the largest fish kill recorded in Maryland so far this year.

This fish kill is the second such event in Anne Arundel County waters in recent weeks. On Aug. 20-21, more than 2,000 fish died in the Magothy River's Blackhole Creek.

The estimate of 100,775 dead menhaden in Aberdeen Creek is up from the initial estimate of 37,000 given by MDE.

The small, dead fish dotted the water like flower petals yesterday afternoon. Piles of the fish littered the shoreline. The smell of dead fish hung in the air and seagulls dropped in for a meal.

"It was sort of blanketed along the shoreline," said Bill Goldsborough, a senior scientist with the

Chesapeake Bay Foundation.

Menhaden are small, filter-feeding fish that are not generally eaten by humans.

There is a small commercial fishery in Maryland's portion of the Chesapeake Bay, where the fish are caught and sold as bait. In Virginia's portion of the bay, there's a large industrial harvest of menhaden that are used in nutritional supplements, pet food and other products. Activists have tried to curtail that harvest.

Menhaden play an important role in the ecosystem. They gobble up algae and, in turn, get eaten by bluefish, rockfish and other large fish.

The dead fish were all "young of year" fish, also called "peanut bunkers," Mr. Goldsborough said.

Menhaden spawn their young in the ocean and then the larvae are washed into estuaries like the Chesapeake Bay. The young develop through the spring and by summertime, they swim in schools in the bay's rivers and creeks.

"It would make these about 8 months old," Mr. Goldsborough said.

Kills happen when there's a dramatic reduction in dissolved-oxygen levels in the water and fish can't escape to healthier water.

There are multiple reasons why the oxygen drops, though it's usually due to an algae bloom. Decaying algae sucks oxygen from the water.

Many fish need 5 mg of dissolved oxygen per liter of water to survive. Crabs need 3 mg/l and some worms can survive at 1 mg/l.

In this case, MDE officials are testing water samples and fish tissue samples for algae.

During the day, the algae's photosynthesis adds oxygen to the water. But when the sun goes down, the algae sucks oxygen from the water, Mr. Goldsborough said.

At the same time, the fish also are taking oxygen from the water. It's possible there just wasn't enough oxygen to go around.

The site of the fish kill is a secluded cove that doesn't have a strong tide.

"Everything combined to drive dissolved oxygen to lethally low levels," said Kim Lamphier, an MDE spokesman.

While the increases and decreases of oxygen are somewhat of a natural process, Mr. Goldsborough said the situation is made worse because human activities promote algae growth. Nitrogen and phosphorus from fertilizer, stormwater runoff, old septic systems and sewage plants fuel the growth of algae.

Mr. Goldsborough likened the fish kill to a "mini dead zone" - just like the oxygen-deprived stretch of water in the main portion of the bay, only smaller.

"All those things together lead to a fish kill like this," he said.