Pollution has reduced the grasses to only 10% of their historic levels, from 600,000 acres to around 65,000 acres today. Another problem occurs when algae dies and begins to decompose. The process of decomposition removes dissolved oxygen from the water and turns large sections of the Bay into dead zones where life can not be supported.
The presence of phosphorus in the Chesapeake Bay has been receiving extra attention because of its possible role in outbreaks of the toxic microbe pfiesteria. Pfiesteria is suspected to cause lesions on fish in the Bay. There are currently studies underway searching for a correlation between fertilizer runoff and the outbreak of Pfiesteria.
Toxins, such as the heavy metals mercury, cadmium, copper, lead, zinc; and pesticides, dioxins, polychlorinated biphenols (PCBs), polynuclear aromatic hydrocarbons (PAHs), and many other chemicals have been identified as a potential threat to the Bay. Toxic substances are poisonous to humans and other living things and have been known to cause a wide range of negative health effects. There are over 70,000 chemicals currently in use. Less that 2% of these chemicals have been adequately tested for their impact on human health and the environment. The testing, monitoring, and controlling of toxic substances is very complex and expensive. As a result, not enough is known about the kinds and amounts of toxic chemicals entering the Bay or the effects they have on the living things in the Bay's water.
There are three basic ways that pollution gets into the Chesapeake Bay. The first is point source discharges such as sewage treatment plants, industrial facilities, and food production and processing facilities. They discharge nutrient and toxic-laden wastes, often through pipes, directly into the water. Some facilities carry their wastes off site and spread them across the land, where they eventually flow into the water.