Glossary of Acronyms, Phrases, Terms, and Units


AIS - Aquatic Invasive Species. See definition.
Aeration - To force or supply water with air, usually to alleviate low dissolved oxygen conditions in water bodies.
Aerobic - A condition in water where dissolved oxygen levels are high. Also refers to aquatic life or chemical processes that require oxygen.
Algal bloom - An unusual or excessive abundance of algae.
Anaerobic - A condition in water where dissolved oxygen levels are low.
Anoxic - A condition in water where dissolved oxygen levels are low.
Aquatic Invasive Species - Species in an aquatic environment where they can easily out compete other species. Usually causes a disruption in the balance of a ecosystem. Oftentimes the species is an exotic. Examples of exotic aquatic invasive species in the CRWD are curly-leaf pondweed and eurasian watermilfoil.
Aquifer - An underground layer of water-bearing rock or an unconsolidated material deposit (gravel, sand, silt) that can yield a usable quantity of groundwater.


Benthic - The bottom layer or zone of a waterbody (primarily found in lakes). Can also refer to life forms that dwell in this zone.
Best Management Practice - A control, treatment, and/or management technique, system, or project whereby the best practice for a specific physical area is put in place to realize a benefit in the control and/or abatement of pollution. Common examples of Best Management Practices are: grassed waterways, filter strips, infiltration systems, retention ponds, shoreline restoration projects, tile intake buffers, etc.
Biochemical Oxygen Demand - The amount of dissolved oxygen needed by aerobic biological organisms in a water body to break down organic matter. The amount varies dependent on temperature and time.
BMP - Best Management Practice. See definition.
Board of Water and Soil Resources - The State of Minnesota's soil and water conservation agency.
BOD - Biochemical Oxygen Demand. See definition.
Buffer - A strip of undisturbed vegetation of various size and type that serves to slow and/or retain surface runoff, thereby lowering the amount of pollutants entering a waterbody.
BWSR - Board of Water and Soil Resources. See definition.


CFS - Cubic Feet per Second. See definition.
CFU/100 mL - Colony Forming Units per 100 Milliliters. See definition.
Chlor-a or Chl A - Chlorophyll-a. See definition.
Chlorophyll-a - A form of the pigment needed for photosynthesis found in plants. A measurement used to determine the amount of photosynthesizing plants in a sample. This measurement assists in determining the quality of the water sampled from. See your lake's report card to find your lake's Chlorophyll-a measurements.
Colony Forming Units per 100 Milliliters - A measurement used to determine the numbers of viable bacterial or fungal cells in water.
CRWD - Clearwater River Watershed District.
Cubic Feet per Second - A measurement used to determine the amount of flow in a moving body of water (i.e. streams, rivers, channels, etc.) This measurement helps in determining the amount of nutrients moving through a water system.


Department of Natural Resources - The State of Minnesota's natural resource conservation and management agency.
Dissolved Oxygen - A measurement used to determine the amount of oxygen dissolved in water. The amount of dissolved oxygen in water is subject to a number of factors, from water mixing to decomposition rate of organic matter.
District - Clearwater River Watershed District.
Diversion Canals, Channels, and Ditches - Constructs used to divert water towards/away from a area. Used in several of the District's Wetland Treatment Systems.
DNR - Department of Natural Resources. See definition.
DO - Dissolved Oxygen. See definition.


Environmental Protection Agency - A Federal agency tasked with protecting human health and the environment.
EPA - Environmental Protection Agency. See definition.
Epilimnion - The less dense, warmer layer of water on top of a stratified water body, laying above the thermocline. Since it is at the top of the water body, it receives ample amounts of oxygen from wind mixing, along with enough sunlight for plant growth to occur. See Stratification.
Eutrophic - A type of trophic state of water where the water body has high nutrient levels. These waters are sometimes associated with low dissolved oxygen levels and frequent algal blooms.
Eutrophication - A natural, slow-aging process by which water bodies are enriched with plant nutrients. Over the long-term, this results in character changes to the water body. Human activity can accelerate the process - this is known as cultural eutrophication.
Exotic Species - Species introduced into habitats where they are not native.
External Load - The amount of nutrients entering a water body from its watershed. Can be natural or human in origin.


Feedlot - A lot, building, or group of buildings used for confined feeding, breeding, and/or holding of animals for agriculture. These areas usually have manure accumulation and lack of vegetative cover. As such, pastures are not considered to be feedlots.


Gallons Per Minute - A measurement used to determine the amount of water moving through a system. Oftentimes used in wastewater treatment systems.
GPM - Gallons Per Minute. See definition.
Groundwater - Water located beneath the earth's surface in the space between soil particles and in the fractures of rock formations. It is replenished primarily by precipitation, which infiltrates into the ground. Groundwater discharge to surface waters allows streams to flow and sustains lake levels during dry periods.


Hardness - A measurement describing the amount of calcium and magnesium in a water body.
Hydrograph - A graph showing the rate of flow versus time at a certain point in an moving body of water. The rate of flow is typically in cubic feet per second.
Hydrologic Boundary - A physical boundary (usually shown on a map) depicting where water on a surface will drain to. Also known as a watershed, the boundary depicts an area where all flowing water will congregate to, given enough water quantity. In the CRWD, all flowing water will congregate to the Clearwater River, hence the name the Clearwater River Watershed District. See also Watershed.
Hydrology - The study of the properties, distribution, and circulation of water in the atmosphere and upon and below the ground.
Hypolimnetic Aeration - The forced supply of oxygen to the hypolimnion in a water body by artificial means.
Hypolimnion - The dense, bottom layer of water in a stratified water body, laying below the thermocline. In a lake, it typically is the coldest layer in the summer months, and the warmest layer during the winter. Since it is at depth, it is isolated from wind-mixing, and as such oftentimes become anoxic due to lack of air mixing and decomposition of organic matter in bottom sediments. See Stratification.


Internal Load - The amount of nutrients present in a water body bottom sediments. During times of anaerobic or anoxic conditions in a water body, the bottom sediments will oftentimes release their nutrients into the water column. The amount of Internal Load in a water body is affected by the external load to the water body.
Invasive Exotic Species - Species present in an area where they are not native and can cause economic or environmental harm and/or harm to human health.
Impervious Surface - Landforms that effectively block the infiltration of water into the ground. Natural landforms that exhibit this characteristic include certain types of exposed bedrock. Man-made forms include most buildings and pavements for things such as roads and sidewalks. Land that have been significantly altered by human activities will oftentimes exhibit various levels of impermeability.




Lake Management - The process of studying, assessing, and laying out a plan dictating the management of a lake as a natural resource and a sustaining ecosystem.
Littoral - The shallow area of water in a water body dominated by aquatic plants. In Minnesota the littoral zone is defined as the portion of the water body that is less than 15 feet in depth. The majority of aquatic plants grow in this area, and it is a essential habitat for a healthy lake ecosystem.


Meandered Lake - A body of water located within the meander lines shown on surveyed plats made by the US General Land Office.
Mesotrophic - A type of trophic state of water where the water body has medium nutrient levels, between oligotrophic and eutrophic water bodies. These water bodies are often clear with aquatic plants.
mg/L - Milligrams per Liter. See definition.
Micrograms per Liter - A unit of measurement equal to one millionth (1/1,000,000) of a gram, or 1/1,000 of a milligram per one liter. Used in measuring the amount of certain nutrients in water samples.
Milligrams per Liter - A unit of measurement equal to one thousandth (1/1,000) of a gram per one liter. Used in measuring the amount of certain nutrients in water samples.
Milliliters - A unit of measurement equal to one thousandth (1/1,000) of a liter. Used in measuring the amount of certain nutrients in water samples.
Minnesota Pollution Control Agency - The State of Minnesota's pollution control agency.
mL - Milliliters. See definition.
MPCA - Minnesota Pollution Control Agency. See definition.


National Pollutant Discharge Elimination System - The primary permitting program under the Federal Clean Water Act, which regulates all discharges to surface water from point sources.
Native Species - A species that is naturally present in an area.
Natural Resource Conservation Service - An agency of the US Department of Agricultural, the NRCS provides leadership in a partnership effort to help citizens conserve, maintain, and improve the country's natural resources and environment. Most NRCS field offices are located with the county's SWCD offices.
NCHF - North Central Hardwood Forest. See definitions.
Non-meandered Lake - A body of water that is not located on surveyed plats made by the US General Land Office, nor was listed as a navigable water during the time Minnesota became a state. For more information, click here and here.
Non-permitted Sources - Sources of water pollution that do not have to undergo a permitting process, unlike sources such as municipal wastewater treatment plants, which are subject to permitting programs. These sources are typically non-point in nature.
Non-point Sources - Sources of water pollution that cannot be define to a single point. Examples of non-point sources are streambank and lakeshore erosion, agricultural field runoff, and stormwater runoff.
North Central Hardwood Forest - One of seven ecoregions in Minnesota. Ecoregions are areas of relative homogeneity characterized by distinctive regional ecological factors, including land use, soils, topography, ad potential natural vegetation. All of the CRWD is listed in this region.
Notch Weir - A water quality improvement construction, used to temporarily impound water from a designed rain event (typically no greater that 2 inch event) over a couple of days to allow particulate phosphorus to settle out of the water column before entering downstream waters. The notch is a rectangular cut in the weir (or dam) that allow a small amount of water to pass through at a uniform rate, thereby achieving a temporary rather than permanent impoundment.
NPDES - National Pollutant Discharge Elimination System. See definition.
NRCS - Natural Resource Conservation Service. See definition.
Nutrient - A substance, such as Phosphorus and Nitrogen, that act as food/fuel source for the base of a food web in an ecosystem. Too much of these nutrients can have a detrimental effect on water quality, leading to lake eutrophication.
Nutrient Cycling - The yearly cyclical nature of the release of nutrients into the water column from the water body's internal load.


Oligotrophic - A type of trophic state of water where the water body has low nutrient levels. These water bodies often are very clear due to a lack of nutrients for aquatic plants and algae, and typically has high dissolved oxygen levels throughout the water column.
Ortho-P - Ortho Phosphorus. See definition.
Ortho Phosphorus - A measurement of the amount of soluble phosphorus (nutrient) in a water sample.
Oxygen Demand - A measurement of the amount of dissolved oxygen needed by various processes, such as biological or sediment oxygen demand.


pH - The scale by which the acidity or basic nature of a water body is measured. Even slight changes in pH can have an effect of the health of an aquatic ecosystem.
Point Sources - Sources of pollutants that can be defined to a single point, such as industrial wastewater, municipal stormwater, or large feedlot operations.
Pollutants - General terms for various types of substances that cause harm to a natural resource.



Riparian - Land that is adjacent to a water body.
Runoff - The portion of precipitation or irrigation water that flows off of the land and enters surface waters rather than being used or absorbed. Runoff is oftentimes rich in pollutants if not treated first.


Secchi Depth - The quantitative results from using a secchi disk to measure the visible depth of a water body.
Secchi Disk - A measuring tool used to determine the water clarity in a water body by seeing how deep a white disk can be dropped in a water body before it is no longer visible to the naked eye. The depth where visibility is lost is the secchi depth, and this measurement can be used to establish long-term trends on water quality, since clarity is a good indicator of the quality of the water.
Sedimentation - The natural process by which sediment enters a water body from its watershed. This process can be accelerated by various human actions, and is closely related to eutrophication.
Sediment(ation) Basin - A water quality improvement construction, used to capture sediment in water before it enters a downstream water body. The basin allows the sediment in the water to settle to the bottom. As such, sedimentation basin eventually have to be cleaned out to remain effective.
Sediment Oxygen Demand - The sum of all biological and chemical processes in sediment that use oxygen.
Sinuosity - A measure of deviation of a path between two points from the shortest possible path, given by the ratio of {actual path length (or channel length) / shortest path length (or downslope length)}. This measure is use to determine the degree of meander (or bend, curve, wind) in a given length of stream or river channel, whether natural or constructed.
SOD - Sediment Oxygen Demand. See definition.
Soil and Water Conservation District - A county-level unit of government tasked with providing leadership and management of natural resource programs at local levels. SWCDs work alongside other entities to achieve natural resource conservation goals.
Stratification - Water bodies oftentimes undergo a natural process throughout the year where their waters go from a mixed state to a stratified state (and vice versa). Stratification is caused by changes in temperature, with warmer water being less dense that colder water. The warmer layer of water (called the Epilimnion) will sit on top of the colder water (called the Hypolimnion), with a small dividing layer between the two called the Thermocline. In deeper District lakes, stratification is normally a semi-permanent feature, with spring ushering in stratification, and fall ushering stratification out. Stratification can create problems in lakes, with the potential for fish die-offs and excessive plankton growth. For more information on stratification, click here and here.
Subwatershed Area - A term for a watershed nested inside a bigger watershed. A subwatershed can be defined differently dependent on the criteria used. For example, the CRWD is a subwatershed of the bigger Mississippi (St. Cloud) Watershed, which is a subwatershed of the even bigger Mississippi Headwaters watershed, and so on. For District purposes, we have the District divided into fourteen subwatersheds. Those fourteen subwatersheds make up five bigger subwatershed, listed by the EPA.
Suspended Solids - A term for the particulate (not soluble or dissolved) material in the water column, and therefore not settled out to the bottom sediments.
SWCD - Soil and Water Conservation District. See definition.


Trophic State - A measure of the general productivity in a water body, usually determined by measuring the quantities of nutrients and algae in a water body, either by direct or indirect means. Secchi Disc measurements can also be used.
Thermocline - The middle layer of water between the Epilimnion and the Hypolimnion in a stratified water body. This small layer forms as a water body enters into a stratified state. It is a thin layer where water temperature changes more rapidly with depth than does the other layers. It can be seen as the lid that keeps the colder bottom waters from mixing with the warmer upper waters. See Stratification.
TMDL - Total Maximum Daily Load. See definition.
Total Maximum Daily Load - A calculation of the maximum amount of a pollutant that a water body can receive and still meet water quality standards. TMDLs are required under section 303(d) of the Federal Clean Water Act.
Total Phosphorus - A measurement of the amount of all phosphorus (nutrient), soluble and particulate, in a water sample.
Total Suspended Solids - A measurement of all particulate material in a water sample. Used to assist in determine the water quality of the sampled water body.
TP - Total Phosphorus. See definition.
TSS - Total Suspended Solids. See definition.
Turnover - The process by which lakes destratify and mix, due to a changing of water temperature caused by the changing of the seasons. In most central Minnesota lakes, there occurs at least two turnover events, in the Spring and Fall of each year. Some shallow lakes never fully experience a stratified state (i.e. are constantly in a state of mixing, usually due to wind), and as such never experience turnover. It is possible for a lake to have multiple turnover events, depending on it's location, climate, and various other factors.


ug/L - Microgram per Liter. See definition.


V-notch Weir - A water quality improvement construction, used to temporarily impound water from a designed rain event (typically no greater that 2 inch event) over a couple of days to allow particulate phosphorus to settle out of the water column before entering downstream waters. The notch is a v-shaped cut in the weir (or dam) that allow a small amount of water to pass through a decreasing rate, thereby achieving a temporary rather than permanent impoundment.


Water Column - A conceptual column of water from the surface to the bottom sediments.
Watershed - A land surface area that drains into a water body. Watersheds vary in size, from small catchment basins (like ponds and lakes) to large river basins (like the Mississippi or Ohio River basins). Click here to learn more about watersheds.
Water Table - The depth beneath the earth's surface where the ground is completely saturated with water. The water table depth is not uniform and is variable depending on location.
Wetlands - An area of land that has mostly wet soil, is saturated with water either above or just below the surface for part of the year, and is covered with plants that have adapted to wet conditions. Click here and here to learn more.