303(d) list of threatened and impaired waters

Under Section 303(d) of the Clean Water Act (CWA), states, territories, and authorized tribes are required to develop lists of impaired waters every two years in even-numbered years. The states identify all waters where required pollution controls are not sufficient to attain or maintain applicable water quality standards. States are required to establish priorities for development of TMDLs for waters on the 303(d) List. The TCEQ is responsible for preparing the Section 303(d) list for the state of Texas, and it submitting it to the EPA for final approval. (Related: Texas Integrated Report)


An acre-foot of water covers 1 acre of land 1 foot deep; 43,560 cubic feet; 325,851.4 gallons


Life forms or processes that require the presence of oxygen.


Life forms or processes that occur in the absence of oxygen.


A layer of underground rock or sand which stores and carries water.


All of the land area that drains water to a common point such as a lake, river, or stream.

Best Management Practices (BMPs)

A BMP is a technique, process, activity, or structure used to reduce the pollutant content of a stormwater discharge. BMPs may include simple nonstructural methods, such as good housekeeping and preventive maintenance. BMPs may also include structural modifications, such as the installation of bioretention measures. BMPs are most effective when used in combination with each other, and customized to meet the specific needs (drainage, materials, activities, etc.) of a given operation.


All living organisms within an area.


Biochemical Oxygen Demand - A chemical procedure for determining the uptake rate of dissolved oxygen by the microorganisms in a body of water or sample as they break down organic matter. It can be used to gage the effectiveness of wastewater treatment plants, often included within their permits. It is a five-day test and samples are maintained at 20 degrees Celsius in the dark to prevent photosynthesis. The initial and final dissolved oxygen concentrations is the BOD.


A designated area adjacent to and a part of a steep slope or landslide hazard area which protects slope stability, attenuation of surface water flows, and landslide hazards reasonably necessary to minimize risk; or a designated area adjacent to or a part of a stream or wetland that is an integral part of the stream or wetland ecosystem.


cubic feet per second; 450 gallons per minute (gpm); 646,360 gallons per day; for 24 hours: 1.983 acre-feet; for 30 days: 59.5 acre-feet; for 1 year: 724 acre-feet


A combination of removing bends from a meandering river, straightening a river, increasing its depth, or widening its banks to increase flood water carrying capacity.

Clean Water Act (CWA)

The Federal Water Pollution Control Act, commonly referred to as the Clean Water Act (CWA), held the goal to restore and maintain the chemical, physical, and biological integrity of the nation's waters by preventing point and nonpoint pollution sources, providing assistance to publicly owned treatment works for the improvement of wastewater treatment, and maintaining the integrity of wetlands. Enacted originally in 1948, the Act was amended numerous times until it was reorganized and expanded in 1972.


A concern is identified either when a water body does not meet TCEQ’s screening criteria for a parameter that does not have a state surface water quality standard, or when insufficient sampling events have occurred to identify the water body as “not supporting” the surface water quality standards.

Conservation buffers

Conservation buffers or Buffer Strips are small areas or strips of land in permanent vegetation, designed to intercept pollutants and manage other environmental concerns. Buffers include: riparian buffers, filter strips, grassed waterways, shelterbelts, windbreaks, living snow fences, contour grass strips, cross-wind trap strips, shallow water areas for wildlife, field borders, alley cropping, herbaceous wind barriers, and vegetative barriers.


Texas Clean Rivers Program - Senate Bill 818 (SB 818), known as the Texas Clean Rivers Act, was enacted in 1991 by the 72nd Legislature to ensure the comprehensive regional assessment of water quality in each watershed and river basin of the State.

Cubic Foot

7.8 gallons (62.4 pounds) of water

Designated Use

The Texas Commission on Environmental Quality (TCEQ) assigns designated uses for each stream segment. These uses may include: public water supply, contact recreation, aquifer protection, oyster harvesting, and fish consumption. The TCEQ then looks at water quality parameters to determine if the uses are being achieved.


The volume of water (and suspended sediment if surface water) that passes a given location within a given period of time.


Data Management Plan - a document that establishes an overall plan for the data management requirements for a specific project.


Dissolved Oxygen - the relative measure of the amount of oxygen that is dissolved in a median, such as water expressed as either milligrams per liter (mg/L) or percent saturation. Oxygen is produced during photosynthesis and consumed during respiration and decomposition. Oxygen is necessary to sustain life.

Domestic wastewater

Human-generated sewage that flows from homes and businesses.

Drainage basin

A drainage basin is an area in which water, sediments, and dissolved materials drain to a common outlet, typically a point on a larger stream, a lake, an underlying aquifer, an estuary, or an ocean. For example, the Neches River Basin, in which all land area drains into the Neches River. Also called catchment area, watershed, or river basin.


Geographical framework which defines areas of general ecosystem similarity and in type, quality, and quantity of environmental resources. Ecoregions are based on geology, physiography, vegetation, climate, soils, land use, wildlife, and hydrology. In east Texas, we live within the South Central Plains ecoregion (Lufkin, TX) and the East Central Texas Plains ecoregion (Tyler, TX).


Describes the interaction within a community of plants and animals and the physical environment in which they live.


Wastewater (treated or untreated) that flows out of a treatment plant, sewer, or industrial outfall. Generally refers to wastes discharged into surface waters. (Related: Influent, Point-Source Pollution)


Environmental Impact Statement. A document that discusses the likely significant adverse impacts of a proposal, ways to lessen the impacts, and alternatives to the proposal. It is required by the national and state environmental policy acts when projects are determined to have the potential for significant environmental impact.

Environmental assessment

A written environmental analysis which is prepared pursuant to the National Environmental Policy Act to determine whether a proposed action would significantly affect the environment and thus require preparation of a more detailed environmental impact statement.


The water lost to the atmosphere by two processes - evaporation and transpiration. Evaporation is the loss from open areas like lakes and reservoirs; transpiration is water lost from living plant surfaces. Some factors that can effect the evapotranspiration process are solar radiation, surface area of open bodies of water, wind speed, vegetative cover, soil moisture, root depth, reflective land surface and season.

Fecal Coliform Bacteria

A group of bacteria normally found in the intestines of warm blooded animals whose presence is an indicator of polluted water by human or animal wastes. Escherichia coli (E. coli) is a subset of the fecal coliform group.

Field Parameters

Field parameters are water quality analyses that are completed at the sampling site rather than in the lab. They include dissolved oxygen, pH, conductivity and temperature. (also known as physicochemical data)


Geographic Information System - A GIS is a computer system capable of capturing, storing, analyzing, and displaying geographically referenced information; that is, data identified according to location. GIS technology can be used for scientific investigations, resource management, and development planning.


gallons per minute; 1,000 gpm = 2.23 cfs, 4.42 acre-feet per day


Global Positioning System - GPS provides specially coded satellite signals that can be processed in a receiver, enabling the receiver to compute position, velocity and time.


The specific area or environment in which a particular type of plant or animal lives, grows, and interacts within. The interaction of the abiotic and biotic.

Habitat Quality Index

A determination of the habitat quality combining the assessments of the streams physical characteristics and the characteristics of the surrounding environment into one of four categories (“exceptional”, “high”, “intermediate” or “limited”)


The description and study of water bodies such as seas, rivers, and lakes.

Hydrologic cycle

The model that describes the movement of all water on earth, in all of its phases - solid, liquid, and gas.

Hydrologic Unit

The Hydrologic Unit system is a standardized watershed classification system developed by USGS in the mid 1970s. Hydrologic units are watershed boundaries organized in a nested hierarchy by size. (Related: Hydrologic Unit Code)

Hydrologic Unit Code (HUC)

Hydrologic unit codes are a way of identifying all of the drainage basins in the United States in a nested arrangement from largest (Region: Avg. 177,560 sq. miles) to smallest (Subwatershed: Range: 10,000 to 40,000 acres).


The scientific study of the properties, distribution, and affects of water on the earth's surface, in the soil and under ground, and in the atmosphere.

Impaired waterbody

A water body that does not meet one or more of its assigned designated uses due to water quality issues. One or more of the state surface water quality standards is violated.


A natural or man-made containment for surface water.

Indicator organisms

An organism, species, or community that indicates the presence of a certain environmental condition or conditions. Intolerant organisms are sensitive to degradation in water quality and habitat. Tolerate organisms have the capacity to grow and thrive when subjected to unfavorable environmental factors. By looking as these aquatic organisms found within a water body, one can associate whether the water quality has been degraded or is a stable environment for pollution-intolerant species. Because some aquatic organisms have long life cycles and cannot simply move out of an area easily, indicator organisms are useful for displaying water quality past conditions.

Also refers to bacteria such as fecal coliforms, E. coli or enterococcus. The presence of these bacteria indicate possible contamination with other potentially more pathogenic bacteria, such as Salmonella, or viruses, protozoa, or parasites. These indicator organisms are used to test for the presence of fecal contamination.


Water, wastewater or other liquid flowing into a reservoir, basin or treatment plant (Related: Effluent).

Invasive (alien/ non-indigenous) Species

Invasive species are organisms (fish, plants, mussels, etc.) that enter into an ecosystem or habitat beyond their historic ranges. They often aggressively proliferate in this new area because they lack natural predators in the new area. This allows the invading species to out-compete native species for resources, introduce new disease and parasites to the native community, and may alter the established food web. Some examples of invasive alien species are: giant salvinia, common tarp, hydrilla, water hyacinth, nutria, and zebra mussels.


Standing waters, such as lakes, ponds, or bogs.


The study of the physical, chemical, and biological aspects of inland waters.


Running or flowing water systems, such as rivers and streams.


Million gallons per day, a rate of liquid flow.

Native Species

Species that are indigenous (native) to an area.


Nitrate (NO3) and nitrite (NO2) are naturally occurring ions that are part of the nitrogen cycle. Nitrate is used mainly in inorganic fertilizers, and sodium nitrite is used as a food preservative, especially in cured meats. The nitrate concentration in groundwater and surface water is normally low but can reach high levels as a result of agricultural activity and runoff, refuse dump runoff, or contamination with human or animal wastes.

Non-Point Source Pollution

Pollution that is not released through pipes and not regulated. NPS pollution is carried by rainfall or snowmelt moving over and through the ground. As the runoff moves, it picks up and carries any natural and human-made pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters, and even our underground sources of drinking water. Common non-point sources are agriculture, forestry, urban storm water, mining, construction, dams, channels, land disposal, saltwater intrusion and city streets. (Related Terms: Point-Source Pollution)

NPDES: National Pollutant Discharge Elimination System

National Pollutant Discharge Elimination System. The Clean Water Act requires point source discharges to obtain permits. These permits, referred to as NPDES permits, are administered nationally by the Environmental Protection Agency (EPA). In 1998, the TCEQ assumed federal regulatory authority over discharges of pollutants to Texas surface water and has administered the program in Texas under the umbrella of the Texas Pollutant Discharge Elimination System (TPDES). The TPDES program has authority over all discharges of pollutants to Texas surface waters with the exception of discharges associated with oil, gas, and geothermal exploration and development activities, which are regulated by the Railroad Commission of Texas.


The point where runoff discharges from a sewer pipe, ditch, or other conveyance to a receiving body of water.


Chemical, physical, or biological water quality analyses, such as dissolved oxygen or total dissolved solids. Upon entering the data into the Surface Water Quality Information System (SWQMIS), each analysis has its own special parameter code.


Microorganisms that can cause disease in organisms such as humans, animals, and plants. Pathogens include bacteria, viruses, amoeba, fungi, or parasites.


Organisms that cling to surfaces (i.e. rock) or structures (i.e. tire) in the water.

Point-Source Pollution

Pollutant loads discharged at a specific location from pipes, outfalls, and conveyance channels from municipal wastewater treatment plants, industrial waste treatment facilities, sewage bypasses, and oil production areas. Point-source pollution is regulated and permitted. (Related terms : Non-Point Source Pollution)

Point discharge

The release of collected and/or concentrated surface and storm water runoff from a pipe, culvert, or channel. Any point discharge must have a permit issued and approved.


A substance that can cause pollution. Examples include heavy metals or pesticides.


The man-made or man-induced alternation of the chemical, physical, and biological integrity of water.

Potable water

Water that is suitable and safe for drinking.

Riparian Zone

A riparian zone or riparian area is the interface between land and a river or stream. Plant habitats and communities along the river margins and banks are called riparian vegetation or riparian buffer zones. The word "riparian" is derived from Latin ripa, meaning river bank. Riparian zones may be natural or engineered for soil stabilization or restoration. These zones are important natural biofilters, protecting aquatic environments from excessive sedimentation, polluted surface runoff, and erosion.

Rip rap

A facing layer or protective mound of stones placed to prevent erosion or sloughing of a structure or embankment due to the flow of surface and storm water runoff.


Water that flows over the surface of the land when rainfall is not able to infiltrate into the soil, either because the soil is already saturated with water or because the land surface is impermeable (i.e., rock, concrete, asphalt, metal, brick).

Screening Criteria

Water quality criteria established to protect the water body from excessive nutrient enrichment.

Section 303(d) CWA

Section of the Clean Water Act that requires states periodically to identify waters that do not or are not expected to meet applicable water quality standards. These waters are identified on the Sec. 303(d) Impaired Waters List. Once a waterbody is on the 303(d) list, the TCEQ develops a schedule identifying Total Maximum Daily Loads (TMDLs) that will be initiated in the next two years for priority impaired waters. (See Related: Texas Integrated Report)

Section 305(b) CWA

Section of the Clean Water Act that requires states to submit a biennial report in even-numbered years to the U.S. Environmental Protection Agency describing the quality of the state's waters. The Sec. 305(b) report describes the overall water quality conditions and trends in the state. (See related: Texas Integrated Report)

Storm water

Generally, run-off water from land and impervious cover such as paved streets, parking lots and rooftops, generated during rain events which carries pollutants, such as oil, sedimentation and animal waste in quantities that can negatively impact water quality (see stormwater pollution).

Stormwater pollution

Water from rain, irrigation, garden hoses or other activities that picks up pollutants (cigarette butts, trash, automotive fluids, used oil, paint, fertilizers and pesticides, lawn and garden clippings and pet waste) from streets, parking lots, driveways and yards and carries them through the storm drain system and into water bodies.

Stream Segment

Waters designated by the TCEQ in the Surface Water Quality Standards (TSWQS) that include most rivers and their major tributaries, reservoirs, and lakes. Segmented waters have designated four-digit numbers (ex: 0604 Neches River Below Lake Palestine), designated physical boundaries, specific uses, and numerical criteria.

Subsurface Water or Groundwater

Subsurface Water or Groundwater is water that exists below the land surface. It is more protected from evaporation than surface water. Subsurface water is generally stored in the porous spaces within rock, such as the limestone of the Edwards Aquifer or between the particles of gravel and sand that make up the Carrizo-Wilcox aquifer. (see also water table)


A Hydrologic Unit. A river basin is divided into numerous watersheds. These watersheds are then further divided into subwatersheds.

Surface Water

Water that remains on the surface of the land. Examples include rivers, lakes, reservoirs, streams, wetlands, impoundments, seas, estuaries, etc. (Related Terms: Subsurface Water)


The Texas Commission on Environmental Quality. The environmental agency for the state of Texas. Previously named the Texas Natural Resource Conservation Commission (TNRCC), but was renamed in 2002. The Texas Commission on Environmental Quality strives to protect our state's human and natural resources consistent with sustainable economic development. The goal of the TCEQ is clean air, clean water, and the safe management of waste.

Terrestrial Wildlife

Wildlife that spend the majority of their lives on land.

Texas Integrated Report

Formerly called the Texas Water Quality Inventory and 303(d) list, the Texas Integrated Report for Clean Water Act Sections 305(b) and 303(d), more simply know as the Texas Integrated Report (IR) evaluates the quality of surface waters in Texas. The Texas Integrated Report describes the status of Texas’ natural waters based on historical data. It identifies water bodies that are not meeting standards set for their use on the 303(d) list, and provides resource managers with a tool for making informed decisions when directing agency programs.

Threatened waterbody

Any waterbody of the United States that currently attains water quality standards, but for which existing and readily available data and information on adverse declining trends indicate that water quality standards will likely be exceeded by the time the next list of impaired or threatened waterbodies is required to be submitted to EPA.

Total maximum daily load (TMDL)

A Total Maximum Daily Load, or TMDL, is a calculation of the maximum amount of a pollutant that a waterbody can receive and still safely meet water quality standards. For example, the sum of the individual wasteload allocations (WLAs) for point sources, load allocations (LAs) for nonpoint sources and natural background, and a margin of safety (MOS). TMDLs can be expressed in terms of mass per time, toxicity, or other appropriate measures that relate to a state's water quality standard.


The degree to which a substance damages or causes harm to an organism. Acute exposure to a toxic substance refers to a single exposure within a short period of time resulting in severe biological harm or death. Chronic exposure refers to continuous exposure over an extended period of time causing irreversible side effects.

TPDES: Texas Pollutant Discharge Elimination System



A stream or river that flows into a larger stream or river, and which does not flow directly into a sea.

TSS - Total Suspended Solids

Suspended Solids are solids in water that can be trapped by a filter. Suspended Solids can include a wide variety of material, such as silt, decaying plant and animal matter, industrial wastes, and sewage. High concentrations of suspended solids can cause many problems for aquatic life. Total Suspended Solids (TSS) is a measurement of the suspended solids in a water sample.


A measure of the degree to which water losses its transparency due to the presence of suspended particulates. Increases in turbidity may be caused by plants, sediments, urban runoff, or waste discharge. Because suspended materials absorb heat from the sunlight, turbid waters may have higher temperatures, which can result in lower dissolved oxygen concentrations.


An underlying layer of vegetation, especially the plants that grow beneath a forest’s canopy.


Any water that has been adversely affected in quality by anthropogenic influence. This includes water that has been used for domestic, agricultural, and industrial purposes. Commonly, it refers to municipal wastewater which contains a variety of contaminates resulting from the mixing of wastewater from several sources.

Water quality criteria

Elements of state water quality standards expressed as constituent concentrations, levels, or narrative statement, representing a quality of water that supports a particular use.

Water quality standards

State or federal law or regulation consisting of a designated use or uses for the waters of the United States, water quality criteria for such waters based upon such uses, and an antidegradation policy and implementation procedures. Water quality standards protect the public health or welfare, enhance the quality of water and serve the purposes of the Clean Water Act.

Water rights

A legally protected right to take possession of water occurring in a natural waterway and to divert that water for beneficial use.

Water table

The level below the land surface at which the subsurface material is fully saturated with water. The depth of the water table reflects the minimum level to which wells must be drilled for water extraction.


A drainage basin includes an area in which water, sediments, and dissolved materials drain to a common outlet, typically a point on a larger stream, a lake, an underlying aquifer, an estuary, or an ocean. A watershed encompasses a broader view of a drainage basin, and includes climate, precipitation, geology, geography, and human activities as water flows into the common outlet.


An area that is regularly saturated by surface or groundwater and characterized by vegetation adapted for life in saturated soil conditions. Marshes, swamps, bogs, and fens are categories of wetlands. Some important functions of wetlands include: the filling of water during flood/ other storm events, sediment stabilization, flood attenuation, and nutrient cycling. Wetlands can be described as transitional zones between uplands and deep water and are protected ecosystems regulated by the United States Army Corps of Engineers (outlined in section 404 of the CWA).