Phytoplankton populations in the Bay are an excellent indicator of nutrient pollution, as well as efforts to reduce pollution. Phytoplankton respond quickly to changes in nutrient levels, which gives researchers a good indication of the Bay’s health.

An airshed is an area of land where pollution released into the air can eventually wind up in a specific water body. Airsheds can be very large. For example, the Chesapeake Bay’s nitrogen oxide (NOx) airshed is 570,000 square miles, stretching west to Ohio and north to Canada.

Water clarity improves when less pollution washes off the land and into streams, rivers and the Chesapeake Bay. You can help improve water clarity by fertilizing your lawn less and planting a buffer of trees and shrubs around your property. Also, when boating, make sure you obey wake laws so you don’t stir up bottom sediments in shallow areas.

Poor water clarity is usually caused by a combination of suspended sediments, organic matter and excess nutrients that fuel the growth of water-clouding algae. Weather also plays a large role in water clarity. Rain storms can wash dirt and pollutants into the Bay and cause the water to look muddy. During drier conditions, the water is usually clearer.

Sometimes the Bay’s deeper waters have little or no oxygen while surface waters have more oxygen. This usually happens in summer because of a combination of factors, including temperature, nutrient pollution, the way water flows in the Bay, and the shape of the Bay’s bottom.

Temperature, nutrient pollution, the way water flows in the Bay, and the shape of the Bay’s bottom all interact with each other to affect the amount of oxygen in the water.

People contribute pollution that can cloud the water and block sunlight from reaching bay grasses. This pollution comes from many sources, including farms, sewage, fertilizer and development.