USEPA Office of Water - TMDL Program Results Analysis Fact Sheet - July 17, 2009
Fact Sheet: Introduction to Clean Water Act
(CWA) Section 303(d) Impaired Waters Lists
What is a 303(d) list of impaired waters?
The goal of the Clean Water Act (CWA) is "to restore and maintain the chemical, physical, and biological integrity of the Nation's
waters" (33 U.S.C §1251 (a)). Under section 303(d) of the CWA, states, territories, and authorized tribes, collectively referred to
in the Act and here as "states," are required to develop lists of impaired waters. The term "303(d) list" is short for the list of
impaired and threatened waters (e.g., stream/river segments, lakes) that all states are required to submit for EPA approval
during even-numbered years. The main program result of this process is EPA's national tracking system for impaired waters.
A state's 303(d) impaired waters list is comprised of all waters where the state has identified that required pollution controls are
not sufficient to attain or maintain applicable water quality standards. The law requires that states establish a prioritized
schedule for waters on the lists, and develop Total Maximum Daily Loads (TMDLs) for the identified waters based on the
severity of the pollution and the sensitivity of the uses to be made of the waters, among other factors (40C.F.R. §130.7(b)(4)).
A TMDL is a calculation of the maximum amount of a pollutant that a waterbody can receive and still safely meet water quality
standards, and an allocation of that load among the various sources of the pollutant. States provide to EPA a long-term plan for
completing TMDLs within 8 to 13 years from the first listing of the waterbody. EPA policy allows states to remove waterbodies
from their 303(d) list after they have developed a TMDL or made other changes to correct water quality problems.
How do states identify impaired waters?
Regulations say states must evaluate "all existing
and readily available information" in developing
their 303(d) lists (40 C.F.R. §130.7(b) (5)). Usually
due to a lack of resources, most state water
quality agencies are able to monitor only a limited
percentage of their waters consistently enough to
detect water quality problems. Many state
agencies use data collected from outside
organizations and the public to compile their lists.
There are usually quality requirements for data
collection and submission before state agencies
will consider the data.
How do states submit lists?
In addition to the 303(d) impaired waters list, the
CWA requires each state report every two years
on the health of all its waters, not just those that
are impaired. Information from this report, known
as the 305(b) report or "biennial water quality
report," has historically been used to develop the
"threatened and impaired waters" (303(d)) list.
Most states compile the data and findings from
the 305(b) report and add information from other
sources to produce the 303(d) list. EPA
recommends that states combine the threatened
and impaired waters list with the 305(b) report to
create an "Integrated Report," due April 1 of even-
numbered years.
Once states submit their 303(d) list to EPA, EPA then has 30 days to approve or disapprove the 303(d) lists. If EPA disapproves
a state list, EPA has 30 days to develop a new list for the state; although historically, EPA has rarely established an entire list for
a state. Sometimes EPA partially disapproves a list because of omission and adds waters to the state's list.
National Summary of Top 303(d) Listing Impairments
EPA's Assessment and TMDLs Tracking and Implementation System (ATTAINS) provides state-reported data on the condition
of monitored surface waters. ATTAINS is the primary result of long-term state and EPA collaboration on tracking,
characterizing, and mapping of 303(d)-listed waters. Below is an excerpt showing the topi 5 causes of impairment for 303(d)
listed waters in ATTAINS. Note that one body of water may have single or multiple listed impairment causes.
Causes of Impairment for 3O3(d) Listed Waters
Mob.3Is i.:.th.-r i-.l-i.-in Mercury ;i
? of Impairment (
Number of Causes of Impairment Reported
Organic EnnchmentyOxvaen Depletion
:ausg Unknown - Impaired Biota
Temperature
Salinity/Total Dissolved Solids •-hl.-.n.l - - Sulfates
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USEPA Office of Water - TMDL Program Results Analysis Fact Sheet - July 17, 2009
How does the 303(d) listing process help to improve water quality?
For many states, identifying waters on a 303(d) list is the first step towards achieving water quality goals. Listing a waterbody on
a 303(d) list requires states to review their water quality standards, evaluate available monitoring data and determine if adequate
controls are in place for point and nonpoint sources of pollutants. States use this information to identify those waters not
meeting the applicable water quality standards (referred to as "impaired waters") or having declining trends (referred to as
"threatened waters"), after pollution controls are in place. By identifying threatened waters, states take a more proactive
"pollution prevention" approach to water quality management.
In many respects, the 303(d) list acts as a "trigger" signaling the need for immediate management actions to address water
quality impairments. Section 303(d) of the CWA also requires states to identify those water quality-limited waters needing
TMDLs and to organize its list of waters in a prioritized schedule for TMDL development. Using the impaired waters listing
process, states have readily available data and determinations on current water quality impairments, and therefore are able to
set management priorities for addressing such impairments accordingly. A 303(d) list effectively influences and guides many
appropriate courses of action for restoring and protecting the waters of the U.S.
Program Results through 303(d) Listings of Impaired Waters
* Guidance to States
• EPA first provided guidance for states developing 303(d) lists in the 1992 issuance of Guidance for Water
Quality-Based Decisions: The TMDL Process.
• EPA continues to provide guidance to states through various Integrated Reporting Guidances (issued for
reporting cycles 2002, 2004, 2006, 2008 and 2010), with the 2006 Integrated Reporting Guidance providing the
most comprehensive level of detail on using the 5 categories.
• Additionally, EPA recognizes unusual listing challenges, such as in listing and addressing waters impaired due
to atmospheric sources of mercury, and has developed specific guidance appropriate to these challenges (see:
Listing Waters Impaired by Atmospheric Mercury).
• Timely Submission and Review of 303(d) Lists/Integrated Reports
Over the past two years, EPA has worked with states to anticipate and address potential issues with the 303(d) list early
on in an effort to streamline the 303(d) list submission process. EPA saw a substantial jump in the number of 303(d)
List/Integrated Report submissions for the 2008 Integrated Report Cycle. Over three times as many lists were received
by the deadline month compared with the 2006 Cycle. Similarly, EPA has made considerable progress in the amount of
time the Agency takes in issuing a final action (approve/disapprove) on a State's list.
• National Information about 303(d) Listed Waters Online
EPA has consolidated several years of states' 303(d) listing into the ATTAINS data system, providing publicly available
information on over 40,000 tracked waters and user-friendly access to data at scales from local to statewide to national.
• National GIS (Mapped) Data on Geo-Referenced Impaired Waters Online
EPA indexes state spatial data to the National Hydrography Dataset Plus (NHDP/us) to
provide a nationally consistent reference layer. The indexed data is housed in EPA's
Reach Address Database (RAD). EPA provides access to a static national shapefile of
303(d) listed waters, as well as dynamic access to individual state or watershed-level
shapefile downloads as new data become available. The spatial data downloads can
be related to tabular data extracted from ATTAINS via the WATERS Expert Query tool.
Additional Resources:
0 For more information on CWA Section 303(d) lists visit: http://www.epa.qov/owow/tmdl/overview.html
0 For more information on EPA's 303(d) Listing Guidance, including the recommended "Integrated Reporting" for
reporting under Sections 303(d) and 305(b) visit: http://www.epa.gov/owow/tmdl/quidance.htmltf2
0 For a national summary or state-by-state data on listed threatened and impaired waterbodies visit EPA's Assessment and
TMDL Tracking and Implementation System (ATTAINS): http://www.epa.gov/waters/ir/index.html
0 For tabular state data on 303(d) listed impaired waterbodies visit EPA's WATERS Expert Query Tool:
http://www.epa.gOV//waters/tmdl/expert guerv.html
0 For Geographic Information Systems (GIS) Downloads visit EPA's Reach Address Database (RAD):
http://epamap32.epa.gov/radims/ or visit the WATERS Data Download page: http://www.epa.gov/waters/data/downloads.html
0 For more information on the TMDL Program Results Analysis Project visit: http://www.epa.gov/owow/tmdl/results or contact
the project leader at norton.douglas@epa.gov
Notice: This fact sheet contains general information about a program of the U.S. Environmental Protection Agency. It does not
constitute Agency policy, regulations or guidance nor supersede or modify existing policy, regulations or guidance in any way.
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