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Assessing and Reporting Water Quality (Questions and Answers)

This fact sheet answers basic questions about how states assess and report on water quality conditions, as summarized in the Water Quality Assessment and TMDL Information website known as ATTAINS.
  1. How do states and other jurisdictions assess water quality?
  2. What is an Integrated Report?
  3. Why did EPA issue guidance to states to integrate their water quality reports?
  4. What are the five Integrated Report categories?
  5. Why aren’t all states integrated?
  6. When will all the state reports be integrated?
  7. What is the difference between the "good," "threatened," and "impaired" categories of use support?
  8. What are "Causes of Impairment"?
  9. What are "Sources of Impairment"?
  10. What kinds of monitoring data are used to make water quality assessments?
  11. Who collects monitoring data?
  12. Is water quality getting better or worse?
  13. How do we determine trends in water quality?
  14. What are statewide statistical surveys?
  15. What is the difference between statewide statistical surveys and site-specific, targeted monitoring?
  16. What is the relationship between the findings of the statewide statistical survey and the state’s site-specific, targeted monitoring program?
  17. What is a Total Maximum Daily Load (TMDL)?
  18. What is the advantage of the Water Quality Assessment and TMDL Information/ ATTAINS website compared to previous ways of depicting state information?
  19. Why are some states missing from rollups for specific reporting cycles (e.g., 2004, 2006) in ATTAINS?
  20. Are data from Tribes and interstate commissions in ATTAINS?

1. How do states and other jurisdictions assess water quality?

Water quality assessment begins with water quality standards. States and other jurisdictions adopt water quality standards for their waters. EPA must then approve these standards before they become effective under the Clean Water Act.

Water quality standards have three elements: the designated uses assigned to waters (e.g., swimming, the protection and propagation of aquatic life, drinking), the criteria or thresholds that protect fish and humans from exposure to levels of pollution that may cause adverse effects, and the anti-degradation policy intended to prevent waters from deteriorating from their current condition.

After setting standards, states assess their waters to determine the degree to which these standards are being met. To do so, states may take biological, chemical, and physical measures of their waters; sample fish tissue and sediments; and evaluate land use data, predictive models, and surveys.

For more information on state water quality standards, visit the National Water Quality Standards website at http://www.epa.gov/waterscience/standards/.

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2. What is an Integrated Report?

An Integrated Report is a biennial state submittal that includes the state’s findings on the status of all its assessed waters (as required under section 305(b) of the Clean Water Act), a listing of its impaired waters and the causes of impairment, and the status of actions being taken to restore impaired waters (as required under section 303(d)).

EPA first issued guidance to the states in 2001 encouraging them to integrate their water quality assessment information into one report. Before the issuance of this guidance, these were separate state 305(b) and 303(d) reports, and in many cases the findings and assessment data in them did not agree. EPA has issued additional guidance on Integrated Reporting in subsequent years.

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3. Why did EPA issue guidance to states to integrate their water quality reports?

The purpose of this guidance was to streamline and reduce the reporting burden to the states and improve the information needed to make water quality management decisions. Information on Integrated Reporting, including the guidance issued by EPA, is available at http://www.epa.gov/owow/monitoring/repguid.html and http://www.epa.gov/owow/tmdl/guidance.html.

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4. What are the five Integrated Report categories?

States are required to place their assessed waters in one of five categories, as follows:

CategoryDescription
1All designated uses (DU) met
2 Some, but not all, DUs met
3 Can not determine if any DUs met
4 Impaired/threatened - TMDL not needed
4a TMDL completed
4b TMDL alternative
4c Non-pollutant causes
5 Impaired/threatened by pollutant - TMDL needed
* Also known as the 303(d) list

A more detailed explanation of the five categories can be found in the 2006 Integrated Report Guidance available at http://www.epa.gov/owow/tmdl/2006IRG/

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5. Why aren’t all the states integrated?

States are as a whole moving toward improved integration of their 305(b) and 303(d) reports. However, EPA guidance on integration is relatively new, and states are not required to integrate their reports. Because 303(d) lists require public comment and EPA approval, this process may delay the development of the 305(b) report, so states may prefer to prepare separate 303(d) and 305(b) reports.

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6. When will all the state reports be integrated?

Since states are not REQUIRED to integrate their 305(b) and 303(d) reports, there may always be some states that do not prepare integrated reports. However, most states are working toward integration.

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7. What is the difference between the "good," "threatened," and "impaired" categories of use support?

Waters rated by the states as "good" fully support all of their designated uses.

Waters rated by the states as "threatened" currently support all of their designated uses, but one or more of those uses may become impaired in the future (i.e., water quality may be exhibiting a deteriorating trend) if pollution control actions are not taken.

Waters rated as "impaired" by the states cannot support one or more of their designated uses.

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8. What are "Causes of Impairment"?

Where possible, states, tribes and other jurisdictions identify the pollutants or stressors causing water quality impairment. These causes of impairment keep waters from meeting the criteria adopted by the states to protect designated uses. Causes of impairment include chemical contaminants (such as PCBs, metals, and oxygen-depleting substances), physical conditions (such as elevated temperature, excessive siltation, or alterations of habitat), and biological contaminants (such as bacteria and noxious aquatic weeds). See also Pollution categories summary document (PDF) (20 pp, 557K, About PDF) for brief, non-technical descriptions of general cause categories.

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9. What are "Sources of Impairment"?

Where possible, states, tribes and other jurisdictions identify where pollutants or stressors (causes of impairment) are coming from. These sources of impairment are the activities, facilities, or conditions that generate the pollutants that keep waters from meeting the criteria adopted by the states to protect designated uses. Sources of impairment include, for example, municipal sewage treatment plants, factories, storm sewers, modification of hydrology, agricultural runoff, and runoff from city streets.

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10. What kinds of monitoring data are used to make water quality assessments?

State water quality assessments are normally based upon five broad types of monitoring data: biological integrity, chemical, physical, habitat, and toxicity. Each type of data yields an assessment that must then be integrated with other data types for an overall assessment. Depending on the designated use, one data type may be more informative than others for making the assessment. For example:

Biological integrity data are objective measurements of aquatic biological communities (usually aquatic insects, fish, or algae) used to evaluate the condition of an aquatic ecosystem. Biological data are best used when deciding whether waters support aquatic life uses.

Chemical data include measurements of key chemical constituents in water, sediments, and fish tissue. Examples of these measurements include metals, oils, pesticides, and nutrients such as nitrogen and phosphorus. Monitoring for specific chemicals helps states identify the causes for impairment and helps trace the source of the impairment.

Physical data include characteristics of water such as temperature, flow, dissolved oxygen, and pH. Physical attributes are useful screening indicators of potential problems, often because they can have an impact on the effects of chemicals.

Habitat assessments include descriptions of sites and surrounding land uses; condition of streamside vegetation; and measurement of features such as stream width, depth, flow and substrate. They are used to supplement and interpret other kinds of data.

Toxicity testing is used to determine whether an aquatic life use is being attained. Toxicity data are generated by exposing selected organisms such as fathead minnows or daphnia ("water fleas") to known dilutions of water taken from the sampling location. These tests can help determine whether poor water quality results from toxins or degraded habitat.

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11. Who collects monitoring data?

Hundreds of organizations around the country conduct some type of water quality monitoring. They also include state, interstate, tribal and local water quality agencies; research organizations such as universities; industries and sewage and water treatment plants; and citizen volunteer programs. Federal agencies such as the EPA and the U.S. Geological Survey, National Park Service and Forest Service also conduct water quality monitoring. They may collect water quality data for their own purposes or to share with government decision makers. States evaluate and use much of these data when preparing their water quality reports.

EPA’s national STORET Data Warehouse is a repository of much of this water quality information. It serves as an archive to protect our investment in water quality monitoring, and provides the interested public and water resource managers access to the wide range of data collected by these many sources.

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12. Is water quality getting better or worse?

It is not appropriate to use the information in this database to make statements about national trends in water quality. The methods states use to monitor and assess their waters and report their findings vary from state to state and even over time. Many states target their limited monitoring resources to waters of interest, and therefore assess only a small percentage of their waters. These may not reflect conditions in state waters as a whole. States often monitor a different set of waters from cycle to cycle. Even weather conditions - such as prolonged drought - can have an impact on whether waters meet their standards from one year to the next.

The science of monitoring and assessment itself changes. We know, for example, that a number of states have increased the amount of fish tissue sampling they conduct and as a result are finding more problems and issuing more protective fish consumption advisories. Improved monitoring, in short, can affect the information in this database by increasing the identification of water quality problems. States may also, over time, change how they issue or report fish consumption advisories.

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13. How do we determine trends in water quality?

National water quality trends are best determined using scientifically-based studies designed to sample water quality conditions at randomly-selected sites that are statistically representative of the Nation's many distinct ecological regions. EPA and the states have embarked on such probability-based studies of near coastal waters; wadeable streams; and lakes, ponds, and reservoirs. The National Coastal Condition Reports use nationally consistent methods and a probability-based design to assess five key indicators of coastal water health. The Wadeable Streams Assessment provides a scientific baseline of stream water quality based on 1,100 randomly-selected sites across the country. The National Lakes Asssesment provides unbiased estimates of the condition of natural and man-made freshwater lakes, ponds, and reservoirs greater than 10 acres and at least one meter deep. Rivers and Streams and Wetlands will also be assessed in coming years.

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14. What are statewide statistical surveys?

Statewide statistical surveys are water quality assessments designed to yield unbiased estimates of the condition of a whole resource (such as all lakes or streams in a state) based on monitoring a representative sample of those waters. They can be used to track trends in water condition at the state scale or sub-state scale. Statistical surveys use standardized methods to quantify, with documented confidence, the extent of water quality problems and the extent of key stressors. Statistical surveys complement more traditional targeted monitoring and assessment programs that generally target only waters of concern or interest.

EPA’s 2010 Integrated Reporting guidance includes a reporting template to help states report the results of their statewide statistical surveys using ATTAINS.

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15. What is the difference between statewide statistical surveys and site-specific, targeted monitoring?

States use two main approaches to assess water quality: statistical surveys and targeted monitoring. Much like opinion polls or indicators of economic health, statewide statistical surveys sample a representative yet randomly selected set of waters of a certain type (e.g., streams and rivers, lakes) and draw unbiased estimates of the condition of all waters of that same type in the state.

Site-specific targeted monitoring, on the other hand, is aimed only at those waters judged to be of concern or interest. Targeted monitoring is used to provide needed information to support management decisions at watershed and local scales (e.g., whether a water meets its water quality standards) for only those individual waters monitored and should not be extrapolated to the larger universe of all of a state’s rivers and streams, lakes, etc.

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16. What is the relationship between the findings of the statewide statistical survey and the state’s site-specific, targeted monitoring program?

There are many differences between statewide statistical surveys and site-specific targeted monitoring, even though it is possible that their findings may appear similar. These differences affect how they are best used to inform water quality management.

The two approaches differ in scope and design. They are assessing two different populations: statistical surveys generate an unbiased estimate of the whole resource (such as all streams), while targeted monitoring addresses only the subset of waters determined by the state to be of concern or particular interest. The two approaches may also differ in method. Statistical surveys use a set of consistent sampling and analytical methods to ensure that results can be aggregated and compared over time. A state’s targeted monitoring program may rely on sampling methods that vary by waterbody or watershed, management need, or over time.

State statistical surveys provide a standardized measure for tracking changes over time and evaluating, at a broad scale, progress in investments to protect and restore water quality. Targeted monitoring provides information on the nature of water quality problems for the subset of those waters that were assessed, allows the state to identify individual waters that are not meeting water quality standards, and helps states set priorities for those waters.

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17. What is a Total Maximum Daily Load (TMDL)?

A Total Maximum Daily Load, or TMDL, is a calculation of the maximum amount of a pollutant that can be present in a segment and still allow attainment of water quality standards, and an allocation of that amount to the pollutant’s sources. The TMDL calculation is TMDL = WLA + LA + MOS, where, WLA is the sum of wasteload allocations (point sources), LA is the sum of load allocations (nonpoint sources and background), and MOS is the margin of safety.

The MOS accounts for any lack of knowledge concerning the relationship between load and wasteload allocations and water quality. The TMDL analysis must take into account critical conditions such as high and low flows and seasonal variations in water quality. The waste load allocation in a TMDL is implemented through NPDES permits, but there is no federal regulatory requirement to implement the allocation to nonpoint sources.

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18. What is the advantage of the Water Quality Assessment and TMDL Information/ ATTAINS website compared to previous ways of depicting state information?

ATTAINS provides one dynamic, continuously updated website where water quality managers and the public can go to view a wide range of state-reported water quality information. ATTAINS for the first time allows the user to view tables and charts that summarize state-reported data for the nation as a whole, for individual states, for individual waters, and for the ten EPA regions. It gives the “full story” showing which waters have been assessed, which are impaired, and which are being (or have been) restored. The user can select the most recent available information or sort by reporting cycle. By displaying Integrated Report data in one location, ATTAINS allows for a more informed summary of the quality of state waters and will provide decision makers with better information on the actions necessary to protect and restore the waters of the U.S.

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19. Why are some states missing from rollups for specific reporting cycles (e.g., 2004, 2006) in ATTAINS?

Some states are missing from cycle-specific rollups in ATTAINS because they either did not submit electronic data for that cycle by a final date required by EPA, or submitted data in a format incompatible with EPA systems. You may be able to find water quality information on that state by visiting the state water quality assessment website.

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20. Are data from Tribes and interstate commissions in ATTAINS?

No. Neither tribes nor interstate commissions are required to submit 305(b) or 303(d) reports to EPA. However, they may have similar information posted on their own websites.

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