In 2007, sales of eggs, chickens and turkeys amounted to $937 million, making poultry the state's biggest agricultural industry, reports Fredericksburg.com.

By one estimate, Virginia's poultry flocks produce about 400,000 tons of manure a year. With the manure from another 101 million birds in Maryland and Delaware, poultry waste has become a major source of nutrient pollution in the Chesapeake Bay.

Nutrients in the Bay cause algae blooms that deplete oxygen in the water. As a result, vast areas of the Bay have become dead zones where fish, crabs and oysters cannot survive. The jobs of thousands of people who once made their living from Chesapeake seafood have been lost while state and federal regulators studied the Bay's problems again and again.

Poultry is not the only source of agricultural nutrient pollution. It also comes from herds of cattle and from fertilizer applied to crops and lawns.

Also, sewage-treatment plants and septic tanks contribute their share of nutrients.

But poultry litter is a special case.

For some reason, birds do not absorb the nutrient phosphorous as well as other creatures and excrete more of it. When poultry manure is applied to farmland for fertilizer, many crops do not absorb all of the phosphorous. Over years, the phosphorous can build up in the soil and eventually leech or run off to fertilize algae blooms in the Bay.

Chemicals used in industrial poultry production are also present in poultry litter, the mix of manure and wood shavings scraped from chicken-house floors.

According to Shenandoah River steward Jeff Kelble, poultry feed contains antibiotics, arsenic and other metals. Bedding is treated with persistent organic pesticides "and highly active estrogenic and androgenic compounds [are] produced by genetically selected poultry animals," he wrote in an e-mail.

Kelble and other environmentalists are concerned that poultry litter may be responsible for fish kills in the Shenandoah and other rivers that eventually flow into the Chesapeake Bay.