algae: Any of various primitive, mainly aquatic, one-or multi-celled, nonflowering plants that lack true stems, roots, and leaves, but usually contain chlorophyll. Algae form the basis of the marine food chain, using photosynthesis to convert carbon dioxide and inorganic nutrients, such as nitrogen and phosphorus, into organic matter. Common algae include dinoflagellates, diatoms, seaweeds, and kelp.

algal bloom: A rapid growth of algae caused by excess nutrients in a body of water. Algal blooms may cause changes in water color. The decay of the algal bloom may reduce the level of dissolved oxygen in the water.

anoxia: The absence of oxygen, or a pathological deficiency of oxygen.

aquifer: An underground layer of rock or soil containing groundwater.

Best Management Practices (BMPs): Management practices (such as nutrient management) or structural practices (such as vegetative buffers) designed to reduce the amount of pollution that rain and snow melt wash from land areas into nearby waters.

critical habitat: Areas that are essential to the conservation of an officially listed endangered or threatened species. Such areas may require special management.

discharge permit: Legal contract negotiated between federal and state regulators and an industry or sewage treatment plant that sets limits on many water pollutants or polluting effects from the discharges of its pipes to public waters.

dissolved oxygen: The amount of oxygen present in the water. More than five parts per million is considered healthy; below three is generally stressful to aquatic organisms.

drainage area: An area of land that drains to one point, also called a "watershed."

eelgrass (Zostera marina): A type of submerged aquatic vegetation.
effluent: Treated or untreated liquid waste material that is discharged into the environment from a point source, such as a wastewater treatment plant or an industrial facility.

estuary: A coastal water resource where freshwater from rivers mixes with saltwater from the ocean.

eutrophication: A process by which a body of water becomes rich in dissolved nutrients, often leading to algal blooms, low dissolved oxygen, and changes in its natural populations.

geographic information systems (GIS): Computer programs that link features commonly seen on maps (such as roads, town boundaries, water bodies) with related information not usually presented on maps, such as type of road surface, population, type of agriculture, type of vegetation, or water-quality information.

groundwater: Water beneath the Earth's surface, between saturated soil and rock, that supplies wells and springs.

hypoxia: A condition of low dissolved oxygen in a body of water.
impaired waters: Surface waters and groundwaters that do not meet normal water-quality standards; "polluted waters."

impervious surface: A surface, such as pavement, that cannot be easily penetrated by water.

loading: The influx of pollutants to a body of water.

mitigation: Actions taken to reduce the negative impacts of a specific land use or activity.

nitrogen: An element that is a component of protein structures in living organisms. Excess nitrogen is a common pollutant in impaired waters.

nonpoint-source pollution: Pollution caused by runoff from diffuse areas having no well-defined source. Nonpoint sources could be on land or in the atmosphere.

nutrients: Chemicals that are needed by plants and animals for growth. In waterways, excess nutrients can reduce water quality by promoting the excessive growth and subsequent decay of plants, especially algae.

parts per million (ppm): A volume unit of measurement; the number of parts of a substance in a million parts of another substance. For example, 10 ppm of nitrate in water means 10 parts of nitrate in a million parts of water.

pathogen: An agent such as a virus, bacterium, or fungus that can cause diseases in humans. Pathogens can be present in municipal, industrial and nonpoint-source discharges.

pH: a measure of acidity or alkalinity, based on a scale of 0 to 14, with 7 being neutral. Acidic readings are lower than 7, alkaline readings are above 7.

phosphorus: An element essential to the growth and development of plants, but which, in excess, can cause unhealthy conditions that threaten aquatic animals.

plankton: Mostly microscopic aquatic organisms (some are barely visible to the naked eye) found in the lighted upper layers of the water column. The type called "phytoplankton" are capable of photosynthesis.

point-source pollution: Water pollution that is discharged from a specific site, such as a pipe, tank, pit, or ditch.

pollutant: A contaminant that adversely alters the physical, chemical or biological properties of the environment. The term includes nutrients, sediment, pathogens, toxic metals, carcinogens, oxygen-demanding materials, and all other harmful substances.

red tide: Discoloration of sea water caused by one-celled algae that produce a substance toxic to many marine vertebrates and to humans who consume contaminated shellfish.

riparian: Relating to the bank or shoreline of a body of water.
runoff: Water that is not absorbed by soil, which drains off the land into bodies of water, either in surface or underground flows.

salinity: The amount of dissolved salts in water, usually expressed in parts per thousand (ppt).

sediment: Particles of sand, clay, silt and plant or animal matter carried in water.

stormwater: Rainwater that runs off the land, usually paved or compacted surfaces in urban or suburban areas, that is often routed into drain systems in order to prevent flooding.

submerged aquatic vegetation: Vegetation rooted in the bed of a body of water (usually no deeper than 10 feet) that normally does not extend above the water surface and usually grows in clusters or beds. It serves as a nursery area for economically important seafood species, and enhances water quality by reducing turbidity and stabilizing sediments. Also referred to as seagrass.

Total Maximum Daily Load (TMDL): The amount of pollution that a body of water can assimilate without violating water-quality standards. Total Maximum Daily Loads are the sum of point-source and nonpoint-source loads.

tributary: A stream or river that flows into a larger stream or river.

turbidity: A measure of water's cloudiness due to suspended and dissolved matter. High levels of turbidity are harmful to aquatic life.
water-quality standards: Established limits of certain chemical, physical, and biological factors in a body of water; water-quality standards differ depending on the designated uses of a waterway.
watershed: The area of land from which rainfall and snow melt drains into a single point. Watersheds are also sometimes referred to as drainage basins or drainage areas. Large watersheds may be composed of several smaller "subwatersheds."

wetlands: Areas that are inundated or saturated by surface water or groundwater, and that support vegetation adapted to saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas.