Glossary of Terms

Algal Bloom

The rapid increase of algae population in an aquatic setting.

Back River

A tidal estuary located about 2 miles east of the city of Baltimore and has a highly developed surrounding area.

Bay Health Index

The average of all seven indicators (chlorophyll a, dissolved oxygen, water clarity, total nitrogen, total phosphorus, aquatic grasses, and Benthic IBI).

Chesapeake Bay

The Chesapeake Bay covers more than 64,000 square miles of water, making it the largest estuary in the United States. The bay lies between the North American mainland on the west and the Delmarva Peninsula on the east. It is fed by more than 150 rivers and streams and flows into the Atlantic Ocean.

Chlorophyll a

An indicator used to measure phytoplankton (microalgae) biomass.

Choptank River

A major tributary of the Chesapeake Bay and the largest river (71 miles long) on the Delmarva Peninsula.

Climate Change

The changing of global and regional climate patterns attributed to an increase of atmospheric carbon dioxide levels produced by fossil fuels.

Conowingo Dam

Located on the lower portion of the Susquehanna River, it measures 102 feet high, and 4,648 feet wide and traps some of the sediments and nutrients from flowing into the Bay.


Also known as blue-green algae, this bacterium obtains its energy from photosynthesis.

Dead zones

Low oxygen (hypoxic) areas in a body of water caused by excessive nutrients that deplete the water of oxygen for aquatic animal species.

Deep channel

Also known as a mid-ocean canyon. A trough-shaped valley of low relief beyond the continental rise on the deep-sea floor.

Deep water

Water depth that is considerably deep and is able to accommodate oceangoing vessels.

Dissolved Oxygen

An indicator that measures how much oxygen is dissolved in the water.


Where a body of water is formed and mixes with freshwater, from rivers and streams, and saltwater from the ocean.


An excess amount of nutrients in a body of water due to land runoff. It causes dense plant growth and reduces oxygen for aquatic animal life.


The reduced oxygen content in a body of water or in the air.

Impervious Surface

Artificial structures like roads, sidewalks, driveways, roofs and parking lots that are covered in materials such as concrete, cement, stones or asphalt.

James River

Located in Virginia, the river is 348 miles long and remains entirely within the state of Virginia. It is one the five largest rivers to flow into the Bay.

Mattawoman Creek

A 30 mile long tributary for the Potomac River.


Water characterized with salinity of 5 to 18‰ (parts per thousand), due to ocean-derived salts.


A source of nourishment that is essential for growth and the continuation of life.


Water characterized with salinity of 0.5 to 5.0‰ (parts per thousand), due to ocean-derived salts.

Open water

Water less than one tenth of which is covered by ice or enclosed by land or other barriers.

Patapsco River

A 39 mile long river located in Central Maryland that flows into the Chesapeake Bay.


Water characterized with salinity of 18 to 30‰ (parts per thousand), due to ocean-derived salts.

Potomac River

A 405 mile long river that drains into the lower area of the Bay. Approximately 5 million people live within the Potomac watershed. This river is one of the five largest rivers that flow into the Bay.


Material that is broken down by weathering or erosion and settles at the bottom of water.

Stormwater Runoff

Water from rain or melted snow that runs off onto the land instead of being absorbed into the ground.

Submerged Aquatic Grasses

Shallow water grasses that do not emerge from the water.

Susquehanna River

Located in the Northeast, the river flows through New York, Pennsylvania, and Maryland and into the northern end of Chesapeake Bay. It provides the Bay with half of its freshwater flow.

Tidal Fresh

Water characterized with salinity of 0-0.5‰ (parts per thousand), due to ocean-derived salts.

Total Maximum Daily Load (TMDL)

The TMDL is a calculation of the maximum amount of a pollutant that a body of water can receive and still meet water quality standards.

Total Nitrogen

An indicator of too much nitrogen in the Bay.

Total Phosphorus

An indicator of too much phosphorus in the Bay.


The rivers or streams that flow into a larger body of water such as a river, bay, or lake.

Turbid Conditions

Water areas that are murky or clouded due to stirred up sediments.


The increase of population from rural areas to urban locations.

Water Clarity

An indicator that measures how much light penetrates through the water.


The area of land where all of the water that is under or drains off it goes into the same place.

York River

A 35 mile navigable estuary located in eastern Virginia and is one of the five largest rivers that flow into the Bay.