Jump to main content.

Great Lakes Glossary

A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z

 Excerpted from the 1994 EPA Report to Congress on the Great Lakes Ecosystem


Acute Toxicity: The ability of a substance to cause poisonous effects that result in severe biological harm or death soon after a single exposure or dose. (See chronic toxicity.)

Administrative Order: A legal document signed by EPA directing an individual, business, or other entity to take corrective action or refrain from an activity. The order describes the violations and actions to be taken and can be enforced in court. Such orders may be issued, for example, as a result of an administrative complaint whereby the respondent is ordered to pay a penalty for violations of a statute.

Adsorption: The adhesion of molecules of gas, liquid, or dissolved solids to a surface.

Advisory: A non-regulatory document that communicates risk information.

Air Pollutant: Any substance in air that could, if in high enough concentration, harm living things.

Algae: Simple rootless plants that grow in sunlit waters in relative proportion to the amounts of light and nutrients available. They are food for fish and small aquatic animals.

Anti-degradation Policies: Part of Federal air quality and water quality requirements prohibiting environmental deterioration.

Areas of Concern (AOC): A geographic area that fails to meet the general or specific objectives of the Great Lakes Water Quality Agreement where such failure has caused or is likely to cause impairment of beneficial use or of the area's ability to support aquatic life. In general, these are bays, harbors, and river mouths with damaged fish and wildlife populations, contaminated bottom sediments, and past or continuing loadings of toxic and bacterial pollutants.

Atmospheric Deposition: Pollution from the atmosphere associated with dry deposition in the form of dust, wet deposition in the form of rain and snow, or as a result of vapor exchanges.


Bacteria: A group of universally distributed, rigid, essentially unicellular microscopic organisms lacking chlorophyll. Some bacteria can aid in pollution control by consuming or breaking down organic matter in sewage or by similarly acting on oil spills or other water pollutants. Bacteria in soil, water, or air can also cause human, animal, and plant health problems.

Benthic Organism (benthos): A form of aquatic plant or animal life that is found near the bottom of a stream, lake, or ocean. Benthic populations are often indicative of sediment quality. The benthos comprise:

  1. Sessile animals, such as sponges, some worms and many attached algae
  2. Creeping forms, such as snails and flatworms
  3. Burrowing forms, which include most clams, worms, mayflies and midges.

Benthic Region: The bottom layer of a body of water.

Bioaccumulative Substances: Substances that increase in concentration in living organisms (that are very slowly metabolized or excreted) as they breathe contaminated air or water, drink contaminated water, or eat contaminated food. (See biological magnification.)

Bioassay: An evaluation using organisms to measure the effect of a substance, factor, or condition by comparing before and after data.

Biological Magnification: Refers to the process whereby certain substances become more concentrated in tissues at each successive stage up the food web. (See bioaccumulative substances.)

Biomass: All the living material in a given area: often refers to vegetation. Algal biomass is often indicative of the trophic status of a water body.

Byproduct: Material, other than the principal product, that is generated as a consequence of an industrial process.


Carcinogen: Any substance that can cause or contribute to the production of cancer.

Chlorophyll-a: The photosynthetic pigment found in most algae. Chlorophyll-a is used to measure the rate of photosynthesis in a body of water.

Chronic Toxicity: The capacity of a substance to cause poisonous effects in an organism after long-term exposure. (See acute toxicity).

Combined Sewers: A sewer system that carries both sewage and stormwater runoff. Normally, its entire flow goes to a waste treatment plant, but during a heavy storm, the stormwater volume may be so great as to cause overflows (combined sewer overflow). When this happens, untreated mixtures of stormwater and sewage may flow into receiving waters. Stormwater runoff may also carry toxic chemicals from industrial areas or streets into the sewer system.

Consent Decree: A legal document, approved by a judge, that formalizes an agreement reached between EPA and Potentially Responsible Parties (PRPs) through which PRPs will conduct all or part of a cleanup action at a Superfund site, cease or correct actions or processes that are polluting the environment, or otherwise comply with regulations where the PRP's failure to comply caused EPA to initiate regulatory enforcement actions. The consent decree describes the actions PRPs will take and may be subject to a public comment period.

Conventional Pollutants: Such contaminants as organic waste, sediment, acid, bacteria and viruses, nutrients, oil and grease, or heat.


Decay: The breakdown of organic matter by bacteria and fungi.

Dissolved Oxygen (DO): The oxygen freely available in water. Dissolved oxygen is vital to fish and other aquatic life. Traditionally, the level of dissolved oxygen has been accepted as the single most important indicator of a water body's ability to support desirable aquatic life.

Drainage Basin: A water body and the land area drained by it.

Dredging: Removal of sediment from the bottom of a water body.


Ecosystem: The interacting system of a biological community and its environmental surroundings.

Effluent: Wastewater--treated or untreated--that flows from a treatment plant, sewer, or industrial outfall. Generally refers to discharges into surface waters.

Emission: Discharges into the atmosphere from such sources as smokestacks, residential chimneys, motor vehicles, locomotives, and aircraft.

Erosion: The wearing away of land surface by wind or water. Erosion occurs naturally but can be caused by farming, residential or industrial development, mining, or timber-cutting.

Eutrophic: The most productive state of a lake, characterized by high nutrient concentrations which result in algal growth, cloudy water, and low dissolved oxygen levels.  (See also Trophic State and Eutrophication

Eutrophication: The process of fertilization that causes high productivity and biomass in an aquatic ecosystem. Eutrophication can be a natural process or it can be a cultural process accelerated by an increase of nutrient loading to a lake by human activity.

Exotic Species: Species that are not native to the Great Lakes and that have been intentionally introduced to or have inadvertently infiltrated the system. Exotics prey upon native species and compete with them for food or habitat.


Fertilizer: Materials, including nitrogen and phosphorus, that provide nutrients for plants.

Food Chain: A sequence of organisms, each of which uses the next, lower member of the sequence as a food source. Members of a chain are interdependent so that a disturbance to one species can disrupt the entire hierarchy.

Food Web: The complex feeding network occurring within and between food chains in an ecosystem, whereby members of one food chain may belong to one or more other food chains.


Game Fish: Fish species caught for sport, such as trout, salmon, or bass.

Groundwater: The supply of fresh or saline water found beneath the Earth's surface, usually in aquifers, often supplying wells and springs.


Habitat: The place where a population (e.g., human, animal, plant, micro-organism) lives and its surroundings.

Heavy Metals: Metallic elements with high atomic weights (e.g., mercury, chromium, cadmium, arsenic, and lead) that tend to be toxic and bioaccumulate.

Herbicide: A chemical pesticide designed to control or destroy plants, weeds, or grasses.


Indicator: An organism, species, or community whose characteristics show the presence of specific environmental conditions.

Insecticide: A chemical specifically used to kill or control the growth of insects.

International Joint Commission (IJC): A binational commission, established by the 1909 Boundary Waters Treaty, with responsibility for decisions regarding obstruction or diversion of U.S./Canadian boundary waters. In 1972 the Commission was tasked with monitoring implementation of the Great Lakes Water Quality Agreement.

J, K, L

Lampricide: A chemical used to kill sea lamprey.


  1. Land disposal sites for non-hazardous solid wastes at which the waste is spread in layers, compacted to the smallest practical volume, and covered with material applied at the end of each operating day.
  2. Land disposal sites for hazardous waste designed to minimize the chance of release of hazardous substances into the environment.

Loading: The addition of a substance to a water body.


Marsh: A type of wetland that does not accumulate appreciable peat deposits and is dominated by herbaceous vegetation. Marshes may be either freshwater or saltwater and tidal or non-tidal. (See wetland.)

Mass Balance Approach: An analytic method, based on conservation of mass, used to assess the quantity and cycling of contaminants throughout a water system.

Mesotrophic: The trophic state of a lake that falls along the continuum somewhere between oligotrophic and eutrophic.  (See also Trophic State and Eutrophication

Metabolite: A substance that is the product of biological changes to a chemical.

Monitoring: A scientifically designed system of continuing standardized measurements and observations and the evaluation thereof.


National Pollutant Discharge Elimination System (NPDES): The national program for controlling discharges of pollutants from point sources (e.g., municipal sewage treatment plants, industrial facilities) into the waters of the United States.

National Priorities List (NPL): EPA's list of the most serious uncontrolled or abandoned hazardous waste sites identified for long-term remedial action under Superfund. A site must be on the NPL to receive money from the Trust Fund for remedial action. This list is based primarily on the score a site receives from the Hazard Ranking System. EPA updates the NPL at least once a year.

Navigable Waters: Waters sufficiently deep and wide for navigation by all or by specified sizes of vessels. Maintenance of navigation is a Federal responsibility carried out by the Army Corps of Engineers.

Nitrate: A compound containing nitrogen and oxygen that can exist in the atmosphere or in water and that can have harmful effects on humans and animals at high concentrations.

Nonpoint Source: Pollution sources that are diffuse and do not have a single point of origin or are not introduced into a receiving stream from a specific outlet. The pollutants are generally carried off land by stormwater runoff. Commonly used categories for nonpoint sources are agriculture, forestry, urban, mining, construction, dams and channels, and land disposal.

Nutrient: Any substance assimilated by living organisms that promotes growth. The term is generally applied to nitrogen and phosphorous, but is also applied to other essential trace elements.

O , P , Q

Oligotrophic: Lakes that are typically cool and clear, and have relatively low nutrient concentrations.  (See also Trophic State and Eutrophication

Permit: An authorization, license, or equivalent control document issued by EPA or a State agency to implement the requirements of an environmental regulation (e.g., a permit to operate a wastewater treatment plant or to operate a facility that may generate harmful emissions).

Pesticide: A substance intended for preventing, destroying, repelling, or mitigating any pest. Also, any substance or mixture of substances intended for use as a plant regulator, defoliant, or desiccant.

Phosphorus: An essential chemical food element that can contribute to the eutrophication of lakes and other water bodies.

Photosynthesis: A process occurring in the cells of green plants and some micro-organisms in which solar energy is transformed into stored chemical energy.

Phytoplankton: That portion of the plankton community comprising tiny plants (e.g., algae, diatoms).

Plankton: Microscopic plants and animals that live in water.

Point Source: A stationary facility from which pollutants are discharged or emitted. Also, any single identifiable source of pollution (e.g., a pipe, ditch, ship, ore pit, factory smokestack).

Pollutant: Any substance introduced into the environment that adversely affects the usefulness of a resource.

Pollution Prevention: Measures taken to reduce the generation of a substance that could be harmful to living organisms if released to the environment. Pollution prevention can be achieved in many ways.

Potentially Responsible Party (PRP): Any individual or company, including owners, operators, transporters, or generators, potentially responsible for, or contributing to, the contamination problems at a Superfund site. Whenever possible, EPA requires PRPs, through administrative and legal actions, to clean up hazardous waste sites that they may have created.

Predator: Any organism that lives by capturing and feeding on another animal.

Pretreatment: Processes used to reduce, eliminate, or alter pollutants from nonresidential sources before they are discharged into publicly owned sewage treatment systems.

Primary Waste Treatment: This treatment consists of the first steps in wastewater treatment during which screens and sedimentation tanks are used to remove most materials that float or will settle. Primary treatment results in the removal of about 30 percent of carbonaceous biochemical oxygen demand from domestic sewage.

Publicly Owned Treatment Work (POTW): A waste treatment facility owned by a State, unit of local government, or Indian tribe.


Record of Decision (ROD): A public document that explains which cleanup alternative(s) will be used at Superfund National Priorities List sites.

Remedial Action Plans (RAPs): Environmental plans aimed at restoring all beneficial uses to Great Lakes Areas of Concern.

Re-suspension (of sediment): The remixing of sediment particles and pollutants back into the water by storms, currents, organisms, and human activities, such as dredging.

Retention Time: The time it takes for the volume of water in a lake to exit through its outlet (i.e., total volume/outlet flow = retention time).

Risk Assessment: qualitative and quantitative evaluation to define the hazards posed to human health and/or the environment.

Run-Off: That part of precipitation, snow melt, or irrigation water that drains off land into surface water. It can carry sediments and pollutants into the receiving waters.


Secondary Waste Treatment: The second step in most waste treatment systems in which bacteria consume the organic parts of the waste. It is accomplished by bringing together waste, bacteria, and oxygen in trickling filters or in the activated sludge process. This removes floating and settleable solids and about 90 percent of the oxygen-demanding substances and suspended solids. Disinfection is the final stage of secondary treatment. (See primary, tertiary waste treatment.)

Sediments: Soil, sand, and minerals eroded from land by water or air. Sediments settle to the bottom of surface water.

Sewage: The waste and wastewater discharged into sewers from homes and industry.

Sewer: A channel or conduit that carries wastewater and stormwater runoff from its source to a treatment plant or receiving stream. Sanitary sewers carry household, industrial, and commercial waste; storm sewers carry runoff from rain or snow; and combined sewers carry both.

Stratification (or layering): The tendency in deep water bodies for distinct layers of water to form as a result of vertical change in temperature and, therefore, in the density of water. During stratification, dissolved oxygen, nutrients, and other parameters of water chemistry do not mix well between layers, establishing chemical as well as thermal gradients.

Superfund: The program under the legislative authority of CERCLA and SARA that carries out EPA's solid waste emergency and long-term remedial activities. These activities include establishing a National Priorities List of the nation's most hazardous inactive waste sites and conducting remedial actions. Sites are cleaned up by potentially responsible parties whenever this can be arranged.

Surface Water: All water open to the atmosphere (e.g., rivers, lakes, reservoirs, streams, impoundments, seas, estuaries) and all springs, wells, or other collectors that are directly influenced by surface water.

Swamp: A type of wetland that is dominated by woody vegetation and that does not accumulate appreciable peat deposits. Swamps may be freshwater or saltwater and tidal or non-tidal. (See wetland.)


Toxic Substance (or toxicant): A substance that can cause death, disease, behavioral abnormalities, cancer, genetic mutations, physiological or reproductive malfunctions, or physical deformities in any organism or its offspring. The quantities and length of exposure necessary to cause these effects can vary widely.

Trophic State (of lakes):  An indication of their biological productivity, that is, the amount of living material supported within them, primarily in the form of algae. The least productive lakes are called oligotrophic. These are typically cool and clear, and have relatively low nutrient concentrations. The most productive lakes are called eutrophic and are characterized by high nutrient concentrations which result in algal growth, cloudy water, and low dissolved oxygen levels. Those lakes with a trophic status that falls along the continuum somewhere between oligotrophy and eutrophy are termed mesotrophic.


Urban Runoff: Stormwater from city streets and adjacent domestic or commercial properties that may pickup terrestrial contamination and carry pollutants of various kinds into sewer systems and/or receiving waters.


Vaporization: The change of a substance from a liquid to a gas.

Volatile Substance: A substance that evaporates readily.


Waste Treatment Plant: A facility containing a series of tanks, screens, filters, and other processes by which pollutants are removed from water.

Wastewater: The spent or used water from individual homes, a community, a farm, or an industry that often contains dissolved or suspended matter.

Watershed: The land area that drains into a river, stream, or lake.

Water Table: The level of groundwater.

Water Quality Standards: State-adopted and EPA-approved standards for water bodies. Standards are developed considering the uses of the water body and the water quality criteria that must be met to protect the designated uses.

Wetland: An area that is regularly saturated by surface water or groundwater and is characterized by a prevalence of vegetation that is adapted for life in saturated soil conditions (e.g., swamps, bogs, fens, marshes, and estuaries).

Wildlife Refuge: An area designated for the protection of wild animals, within which hunting and fishing are either prohibited or strictly controlled.

X, Y, Z

Zooplankton: Microscopic aquatic animals.


Local Navigation

Jump to main content.