DUANE A. SMITH 

EXECUTIVE DIRECTOR 

STATE OF OKLAHOMA 

WATER RESOURCES BOARD 

August 11 , 2008 

Ms. Denise Keehner 

U.S. EPA Headquarters 

Ariel Rios Building 

1200 Pennsylvania Ave., N.W. 

Mail Code: 4305T 

Washington, D.C. 20460 

Dear Ms. Keehner: 

www.owrb.ok.gov 

BRAD HENRY 

GOVERNOR 

It:·has been my pleasure to work with you and your staff over the last several months to clarify 

many fundamental Water Quality Standards issues we have wrestled with in recent years. 

Whether these issues arose through ASIWPCA, WQS Managers Meetings, WQS Workgroup 

Meetings or the WQS Academy, it has been both enlightening and encouraging to explore them 

with you. 

Would it be possible for you to·f-orward -to me in writing the results of some of these discussions 

to share with my staff and state 'colleagues? As an example, we've framed the question of 

"existing uses" with the following questions: 

What are existing uses? 

When determining an existing use, are there situations where a state should 

describe existing uses more specifically than de~i~al:ed uses? 

How should a state determine the existing use for a water body? 

What is the difference between an existing use and a designated use? 

Can a state adopt the existing u·s_e as its designated use? ·· 

We have discussed other foundational issues as well and I would be most interested in affirming 

my understanding of the outcomes of these discussions that reflect our common understanding. 

Thanks again for all 'your time and effort on the critically important work ofWQS. As always 

feel free to call me with any questions at ( 405) 530-8800; · 

Derek Smithee, Chief 

Water Quality Programs Division 

' ' 

CWB 

WAIH! RESOURCES 90AAO the wafer agency 

'3800 N. CLASSEN BOULEVARD • OKLAHOMA CITY, OKLAHOMA 73118 

TELEPHONE (4-05) 530-8800 • FAX (405) 530-8900 

Mark Nichols, Chairman • Rudy Herrmann. Vice Chairman • F. Ford Drummond. Secretary 

Lonnie L. Farmer • Linda Lambert • Richard C. Sevenoaks • Jack Kee!ey • Ed file • Kenneth K Knowles 
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON. D.C. 20460 

Mr. Derek Smithee 

State of Oklahoma 

Water Resources Board 

3800 N. Classen Blvd. 

Oklahoma City, OK 73118 

Dear Mr. Smithee: 

September5,2008 

Of-FICE or 

WAren 

Thank you for your letter of August 11, 2008. I also appreciate the discussions we have 

had with states at ASIWPCA meetings, WQS Managers Meetings, WQS Workgroup meetings, 

and the WQS Academy. You asked if we could forward you in writing the results of these 

discussions to share with your staff and colleagues. Our office is happy to provide you with 

answers to your specific questions that reflect common understanding throughout EPA 

Regional Offices in the enclosed attachment. 

If you have any questions please feel free to contact me at 202-566-1566 or Jim Keating at 

202-566-0383. 

z~ i,~./F~----~~p Denise Keehner, Director 

Standards and Health Protection Division 

Enclosures 

Internet Address (URL) • http://www.epa.gov 

Rt~cycled/Recyclable • Printed w~h Vegetable Oil Based Inks on Recycled Paper (Minimum 30""' Postconsumerl 
Attachment 

I) What are existing uses? 

EPA's regulations define existing uses as " ... those uses actually attained in the water 

body on or after November 28, 1975, whether or not they are included in the water quality 

standards."1

•

2 Existing uses are relevant to two provisions in the Federal regulation - 40 

C.F.R. § 131.10(g), designated uses, and 40 C.F.R. § 131.12(a)(l), antidegradation. 

Overall, these provisions: 

o Prohibit removal of a designated use that would also remove an existing use.3 

o Require the maintenance and protection of existing instream water uses and the 

level of water quality necessary to protect existing uses when implementing a 

state's or tribe's antidegradation policy.4 

EPA considers the phrase "existing uses are those uses actually attained" to mean the 

use and water quality necessary to support the use that have been achieved in the 

waterbody on or after November 28, 1975. Waterbody uses relate to a distinct purpose 

(e.g., recreation, public water supply) or function (e.g., supporting an aquatic ecosystem). 

EPA's regulations, relating to the protection of existing uses, require states and tribes to 

maintain and protect these uses, not specific water quality parameters which may have 

achieved levels more protective than necessary to support these uses.5 

In nearly all cases, a waterbody will have achieved some degree of use related to 

aquatic life, wildlife, and human activity on or after November 28, 1975. States and tribes 

are not bound by their designated use classification categories when describing existing 

uses. In some cases, the use(s) and water quality actually achieved may be less protective 

than the designated use(s) assigned to the waterbody. For example, while the water 

quality since November 28, 1975 may never have been sufficient to support the diverse 

aquatic community associated with the waterbody's designated use, it is likely that the 

water quality in the waterbody supports or has supported some less diverse community of 

organisms. When such uses have been achieved on or after November 28, 1975, EPA 

considers the uses reflecting the degree of aquatic life, wildlife, and human activity 

achieved to be "existing" uses. 

1 40 C.F.R. § 131.3(e). 

2 November 28, 1975 is the date EPA promulgated the initial Federal water quality standards regulations related to 

existing uses. 40 C.F.R. 55334 (Nov. 28, 1975). 3 40 C.F.R. § 131.1 O(g). 4 40C.F.R. § 131.12(a)(l ). 5 In the 1982 preamble to the proposed rule for the current WQS regulations, EPA stated that the first tier of 

antidegradation applies to uses, not specific parameters. For example, if a stream actually achieved a warm water 

fishery use and achieved a dissolved oxygen level of7.0 mg/L, under the existing use regulation the state would 

only be required to maintain the dissolved oxygen levels sufficient to support the warm water fishery existing use 

(e.g. 5.0 mg!L if that is sufficient to support the existing warmwater fishery use). 47 Fed. Reg.49,234, 49,238 

(col. 3)(0ct. 29, 1982). 
A waterbody may have multiple existing uses. When evaluating the uses actually 

achieved along a continuum, the existing uses of a waterbody are the "highest degree of 

uses" and water quality necessary to support those uses, that have been achieved since 

November 28, 1975, independent of the designated use. "Highest degree of uses" 

generally means the degree of use closest to those supported by minimally impacted 

conditions, which usually is associated with the highest level of water quality. In the 

paragraph above, if this less diverse community is the highest degree of aquatic life use 

that has been achieved since 1975, this would be the existing aquatic life use. 

EPA's existing use regulations ensure that the waterbody' s highest degree of uses and 

the necessary levels of water quality actually achieved on or after November 28, 1975 will 

be maintained and protected consistent with the overall objective of the Clean Water Act 

(CW A) to restore and maintain the physical, chemical, and biological integrity of the 

nation's waters.6 Thus, 40 C.F.R. §§ 131.10(g) and 131.12(a)(l) define the absolute 

" floor" or minimum use and necessary level of water quality achieved that must be 

maintained and protected in a waterbody.7 In the above example, where a state is 

designating its uses or revising its designated uses, the state or tribe must ensure that the 

resulting water quality will not jeopardize the less diverse aquatic community (and thus 

the existing use). 

The regulation at 40 C.F .R. § 131.1 O(g) prohibiting removal of an existing use is not 

intended to apply to a situation where the state or tribe wishes to remove a use where the 

removal would result in improving the condition of a waterbody, i.e., facilitates attainment 

of a use closer to those supported by minimally impacted conditions. 8 The intent of the 

regulation is to further the objectives of the CW A "to restore and maintain the chemical, 

physical, and biological integrity" of the nations waters (CW A section 101 (a)), not to 

prevent actions that make the waterbody more like its minimally impacted condition. For 

example, if a pollution tolerant aquatic community is replaced by a more diverse aquatic 

community as a result of improving water quality, loss of the pollution tolerant community 

is a necessary step towards restoring a waterbody to its minimally impacted condition and 

is not a removal of an existing use. Similarly, if a state or tribe stocks trout (a coldwater 

species) into a natural warmwater fishery, the existing use provision would not prevent 

removal of that stocked trout fishery use because a natural warm water fishery is closer to 

the minimally impacted condition. 

Existing use determinations should be made on a site-specific. If a state or tribe can 

show that removing a designated use will not remove an existing use and the state or tribe 

can show that there are factors precluding the attainment of this designated use, the 

state/tribe must then determine and designate the highest attainable use. 

2) When determining an existing use, are there situations where a state or tribe should 

describe existing uses more specifically than designated uses? 

6 CWA section JOI(a). 7 See the preamble to EPA's WQS regulations at 48 Fed. Reg. 51,500, 51,403, col. 2 (Nov. 8, 1983). 

8 See 40 C.F .R. § 13 I .I O(h). States or tribes may remove existing uses where the state or tribe is adding a use 

requiring more stringent criteria .. 
Yes. While there are some situations where it would be reasonable to describe existing 

uses of a waterbody using the same broad categories employed for designating uses, a 

state or tribe should describe existing uses more specifically where necessary to meet the 

intent of the existing use requirements. It would be consistent with the intent of the 

regulation for a state or tribe to more specifically describe its existing use, for example, 

where necessary to maintain and protect unique attributes of a waterbody that are not 

adequately described using a broadly defined designated use category. Examples 1 (CSOimpacted waters) and 2 (mining-impacted waters) provided in the next question, 

demonstrate the importance of describing the existing use (and the water quality necessary 

to support this existing use) in a specific manner so that the uses and the water quality 

improvements achieved since 1975 can be maintained and protected. 

States and tribes must consider existing uses prior to removing or revising a designated 

use and in the context of its antidegradation requirements.9 The Federal regulations do not 

require states and tribes to specify both existing uses and designated uses for each 

waterbod6 in their water quality standards; however a state or tribe may do so if it 

chooses. 1 

3) How should a state or tribe determine the existing use for a waterbody? 

A state or tribe should determine existing uses on a site-specific basis to ensure it has 

identified the highest degree of uses and water quality necessary to support the uses that 

have been achieved since November 28, 1975. When describing existing uses, states and 

tribes should articulate not only the use(s) that has been achieved, but also the water 

quality supporting the specific use(s) that has been achieved. Examples 1 (CSO-impacted) 

and 2 (mining-impacted) below illustrate this point. For aquatic life, states and tribes 

should consider the available biological data as an indicator of both water quality and the 

actual use, in conjunction with any available chemical water quality data. 

Although EPA interprets the definition of "existing use" to require consideration of the 

available data and information on both actual use and water quality, all the necessary data 

may not be available. In these circumstances, a state or tribe may choose, in implementing 

its water quality standards program, to determine an existing use based on the strength of 

evidence that a use has actually been achieved or the strength of evidence that water 

quality supporting a use has been achieved. In other words, where data may be limited or 

inconclusive, EPA expects states and tribes to consider the quantity, quality, and reliability 

of the different types of available data to describe the existing use as accurately and 

completely as possible and to resolve any apparent discrepancies based upon that 

evaluation. As an example, a state is considering removing a primary contact recreation 

use and is therefore evaluating the existing use. While it has information that people are 

swimming in a waterbody, it does not have any data to determine the level of water quality 

that has been achieved on or after November 28, 1975. In this case, the state has two 

9 40 C.F.R. §§ 131.10(g) and 13l.12(a)(I). 

10 EPA notes that 40 C.F.R. § 13 1. 1 O(i) requires states and tribes to "revise its standards to reflect the uses actually 

being attained." 
choices regarding the existing recreation use. If there is no reason to believe that there has 

ever been a water quality problem (e.g., no nearby sources of bacteria), then it would be 

reasonable for the state or tribe to determine that primary contact recreation is the existing 

use. However, ifthere is reason to believe a nearby source may have been limiting the 

water quality since November 28, 1975, the state should conduct a use attainability 

analysis to determine if primary contact recreation is attainable or not. If primary contact 

recreation is deemed attainable, the state must retain primary contact recreation use as the 

designated use, even if it is unclear whether that use is existing. If a primary contact 

recreation use is not attainable, then the state or tribe must designate the highest attainable 

recreation use. 11 

In a 1985 Antidegradation Questions and Answers document, EPA said "An existing 

use can be established by demonstrating that fishing, swimming, or other uses have 

actually occurred since November 28, 1975 or that the water quality is suitable to allow 

such uses to occur (unless there are physical problems which prevent the use regardless of 

water quality.)" While this approach allows states to make an existing use determination 

where it only has information on one or the other type of information, some have 

interpreted this statement as obligating states to ignore one set of information where both 

types are available. EPA has found that, in practice, taking into account all the available 

information results in a more accurate articulation of the existing uses. In addition, the 

1985 policy was stated under the assumption that states and tribes would likely describe 

existing uses in the same terms or categories employed for designated uses. However, 

during the time since issuing those Qs and As, EPA has seen increasingly complex issues 

arise regarding the implementation of the existing use provisions ofthe Federal water 

quality standards regulations. It has become apparent that using the same designated use 

categories to describe existing uses may be insufficiently detailed to accurately describe 

the existing use. 

Under the clarification that states and tribes are not bound to describing their existing uses 

with the same categories employed for designated uses, the following summarizes how 

states and tribes should determine existing uses. 

1. Where a use (i.e., some degree of use related to aquatic life, wildlife, and human 

activity) has actually been achieved on or after November 28, 1975, the existing use 

is the highest degree of use and the water quality that has been achieved and is 

necessary to support the use (see examples 1 and 2); and 

2. Where the water quality achieved was sufficient to support a use on or after 

November 28, 1975, but the use (i.e., some degree of use related to aquatic life, 

wildlife, and human activity) has not occurred, the federal regulations provide states 

and tribes the discretion to determining whether or not this is an existing use. In 

this case, however, it would be reasonable to presume the use is attainable and that a 

state or tribe would need to explain the factors unrelated to water quality (e.g. 

human caused conditions that cannot be remedied, hydrologic modifications) that 

11 40 C.F.R. §§ 131.10(a)-(k). 
are limiting the attainment of the use before it can be removed (see examples 3 and 

4). 

It is appropriate to describe the existing uses of a waterbody in terms of both actual use 

and water quality because doing so provides the most comprehensive means of describing 

the baseline conditions that must be protected. In identifying an existing use, it is 

important to have a high degree of confidence because a state or tribe may not remove an 

existing use when revising designated uses, regardless of whether the existing use remains 

attainable. This is also important because EPA's anti degradation provisions require any 

CW A authorization of a discharge or activity that may result in a discharge to protect the 

existing use.

12 

A specific example given in the 1 985 Antidegradation Qs and As was one of shellfish 

harvesting. In the example, shellfish are thriving, but it is not clear whether people were 

actually harvesting the shellfish. In 1985, EPA said that shellfish harvesting is the existing 

use because to say "otherwise would be to say that the only time an aquatic protection use 

'exists' is if someone succeeds in catching fish." (Appendix G Water Quality Standards 

Handbook). EPA's regulations provide states and tribes the discretion to determine 

whether or not shellfish harvesting is the existing use in this example. While in the 

example there was actual evidence of aquatic life (healthy shellfish), there was no 

evidence of shellfish harvesting. Under EPA's current interpretation, the state or tribe is 

not required to deem shellfish harvesting is an existing use in this situation. A state or 

tribe may determine that the existing use is an aquatic life use that supports healthy 

shellfish but that "harvesting" is not part of the "existing use" since there is no evidence of 

actual harvesting. On the other hand, if shellfish harvesting has not been documented but 

the evidence shows that the water quality to support harvesting has been achieved and the 

shellfish present are (or were) suitable for consumption, a state or tribe may determine the 

existing use is shellfish harvesting or shellfish suitable for consumption. Example 3 below 

further discusses that if water quality supports harvesting, a shellfish harvesting use is 

considered attainable (whether or not the state/tribe has determined it is an existing use) 

and should not be removed, even if no harvesting has actually occurred, unless the state 

can demonstrate otherwise based on one of the 131.1 O(g) factors. 

For example, if shellfish harvesting has not been documented but the evidence shows 

that the water quality achieved and presence of shellfish suitable for consumption support 

harvesting, a state or tribe could determine the existing use is shellfish harvesting or 

shellfish suitable for consumption. Please see examples 3 (shellfish harvesting) and 4 

(public water supply) for further discussion. 

Example I 

People occasionally recreate in a waterbody impacted by combined sewer overflows 

(CSOs). While water quality may be sufficient to support full primary contact recreation 

most ofthe time (i.e., the ambient bacterial densities in the waterbody meet the bacteria 

water quality criteria), the number of indicator bacteria is likely to exceed the water 

12 40C.F.R. § 131.12(a)(J). 
quality criteria established to support primary contact recreation during heavy rainfall 

events that trigger CSO events. If the CSOs have existed before November 28; 1975, what 

is the existing use related to recreation for this scenario? 

In this example, water quality data may show that bacteria levels fluctuated above and 

below the state/tribal criterion for the protection of primary contact recreation and that 

exceedances correlated with the occurrence of CSO events. In addition, data regarding the 

type, timing, and frequency of recreation may show that some recreation (swimming or 

kayaking) occurs regularly in the waterbody even after a CSO discharge when the bacteria 

levels make it unsafe for primary contact recreation. 

Based on the available data for this example, the existing use may be described as a 

primary contact recreation use at times not affected by CSOs and high risk recreation at 

times of CSO overflows (because there is a higher risk of getting sick from pathogens than 

in a water that supports a primary contact recreation use all the time). This existing use 

describes the absolute "floor" or minimum use and necessary level of water quality 

achieved for this waterbody that may not be removed when changing designated uses. In 

addition, the existing use must be protected in the context of antidegradation when 

authorizing a discharge or activity, under the CWA, that is required to meet water quality 

standards (WQS). The WQS existing use regulations, therefore, would not allow 

designated use changes or CW A authorized discharges/activities that would, for example, 

lower the water quality in a manner that would reduce the level of protection to recreators 

achieved by the existing use. Once the state/tribe has determined that changing the 

designated use will not remove an existing use, the state or tribe must conduct a use 

attainability analysis (UAA) if it wishes to change its currently designated recreational use 

to one that would require less stringent criteria. 

Example 2 

Hard rock mining has affected a mountain stream since before November 28, 1975, 

eliminating trout and other native fish, as well as impairing the benthic invertebrate 

community, within 20 stream miles ofthe mining district. Between 1990 and 2000, the 

State undertook a major remediation effort which resulted in a significant reduction in 

most metal concentrations. However, concentrations of cadmium and zinc (year round) 

remain well above the State's acute and chronic numeric criteria adopted to protect the 

trout stream use classification. The State found that with the significant reduction in most 

metals, the benthic invertebrate community fully recovered and the trout and other native 

fish returned to the remediated segment. Yet, the State also found that the number of fish 

per acre was still less than those at similar reference sites and the length/weight index 

showed these trout were not in as good of condition as those in the reference streams. 

Despite the inferior condition of the trout, the lower species numbers, and the fact that the 

water quality was exceeding some of the criteria adopted to protect a trout fishery use 

classification, the return of the trout was enough to encourage the public to fish and thus 

establish a successful trout fishing use. 
In this example, the existing use (i.e., highest degree of aquatic life use and water 

quality necessary to support the use that has been achieved since November 28; 1975) may 

be described as a trout fishery in waters with high levels of cadmium and zinc 

concentrations. In this example, it is likely that maintaining the water quality 

improvements for the most limiting water quality parameters (cadmium and zinc) is 

especially important to maintain the existing use because changes to these parameters are 

likely to correlate with changes in the trout population. 

Example 3 

A waterbody has a healthy shellfish community that is propagating and thriving in a 

biologically suitable habitat and the water quality is sufficient to support both this healthy 

shellfish community and shellfish consumption by humans. However, there is not 

available information indicating that shellfish have been harvested since November 28, 

1975. Because the water quality is sufficient to fully support a healthy shellfish 

community and a shellfish community actually exists, the existing use may be described as 

"a healthy shellfish community" or, as discussed earlier, the state or tribe may choose to 

determine shellfish harvesting is the existing use by weighing the evidence on water 

quality sufficient to support the use and evidence of actual use, and relying on one to a 

greater extent than the other. If the available data are lacking or inconclusive on whether 

shellfish are actually being harvested and consumed, a state or tribe may determine the 

existing use based on a reasonable judgment. 

Shellfish harvesting is a CWA 101 (a)(2) use. Therefore, if a state or tribe is 

considering removing a designated shellfish harvesting use, under 40 C.F.R. § 

131.1 O(j)(2), it must conduct a UAA to demonstrate that shellfish harvesting is not feasible 

to attain due to one of the six factors in 40 C.F .R. § 131.1 O(g), keeping in mind that it 

cannot adopt a use that would lower the water quality in such a way that the water would 

no longer support the existing use. If the water quality is sufficient to support shellfish 

harvesting, it may be difficult to demonstrate that the use is not feasible to attain, even if 

no harvesting has or is occurring. However, 40 C. F .R. § 131.1 O(g) does provide for 

situations where factors other than water quality affect the attainability of a use. Any 

proposed use change must go through a public process consistent with state/tribal law and 

EPA's public participation requirements. 13 

Example 4 

Since November 28, 1975, a particular waterbody has met the human health criteria 

. necessary for a waterbody to be used as a source of public water supply. However, there 

has never been a drinking water intake because the waterbody has never been used as a 

source of drinking water. Is public water supply an existing use for this scenario? 

As stated above, EPA expects states and tribes to look at the available data and 

information on both water quality and actual use to determine if it is an existing use. If 

data are clear that the water quality was sufficient to support a public water supply (PWS) 

13 40C.F.R. §§ 131.10(e) and 131.20(b). 
use, but no PWS use actually occurred since there was no PWS intake, then the Federal 

regulations do not require that the state or tribe find that there is an existing public water 

supply use. EPA recognizes that when states/tribes initially designated uses they may 

have designated certain waters or all state/tribal waters for public water supply use even 

though state, tribal, and local governments have never actually used these waters as public 

water supply sources since November 28, 1975. However, as discussed earlier, states and 

tribes may choose, in implementing their water quality standards programs, to determine 

that a public water supply use is an existing use based on the strength of evidence that a 

use is actually occurring or the strength of evidence that water quality supports a potential 

use. For example, if a use has never occurred in or on the waterbody since November 28, 

1975, but the water quality at the time of evaluation would support such a use, a state or 

tribe may determine that this use is an existing use because maintaining the water quality 

will preserve its use in the future. In addition, where data are unavailable or inconclusive, 

a state or tribe has the discretion to determine whether or not there is an existing public 

water supply use based on best professional judgment. 

4) What is the difference between an existing use and a designated use? 

In 1998, EPA stated that "Designated uses focus on the attainable condition while 

existing uses focus on the past or present condition." 14Existing uses are a description of 

the highest degree of uses and water quality necessary to support the uses that have been 

achieved at any time since November 28, 1975. 15 The existing use identifies a minimum 

use and level of water quality that must be maintained to protect uses that have already 

been attained (i.e, the "floor"). 16 A designated uses, on the other hand, expresses the 

state/tribal objectives (i.e., the highest attainable uses) for a waterbody or set of 

waterbodies. The designated use may or may not have actually been attained in the 

waterbody. 17 In implementing the regulations, it is important to consider both the 

distinction and linkage between designated and existing uses. The following is a 

somewhat simplified example to illustrate how they relate to one another: 

Blue Lake is a relatively small, natural lake. It is fed by tributary streams and has an 

outlet stream that connects it to a larger watershed. Beginning in the 1960s, Blue Lake 

served as a summer retreat and was surrounded by small summer homes with onsite septic 

systems. Over time, as popularity for the vacation spot increased, the area became 

incorporated into a larger urban area. The resulting urban nonpoint source pollution, 

hydrologic modifications to the watershed (increased impervious surfaces), and failure of 

onsite septic systems caused high nutrient and sediment loadings, organic enrichment, and 

low dissolved oxygen (DO) levels in Blue Lake. This led to an increase in nuisance algae 

blooms and loss of submerged aquatic vegetation. The State conducted a biological 

assessment in 1974 which documented poor water quality and that the aquatic community 

14 1998 Advance Notice of Proposed Rulemaking on the Water Quality Standards Regulation. 63 FR 36,742, 36, 

748 (col. 3) (July 8, 1998). 

15 40 C.F.R. § 131.3(e). 16 See the preamble to EPA's WQS regulations at 48 Fed. Reg. 51,500, 51 ,403, (col. 2) (November 8, 1983). 17 40 C.F.R. § 131.3(t). 
was comprised of low numbers of tolerant invertebrate and fish species. Based on this 

information, the State designated a limited warmwater aquatic life use for Blue Lake. 

During the 1980s and 1990s, the community reduced pollutant loadings to Blue Lake 

and water quality and biological conditions improved. Although pollutant loadings from 

urban stormwater remained, connecting the homes to community water and sewer lines 

significantly reduced the organic enrichment and nutrient loadings to Blue Lake. State 

monitoring data showed an increase in water clarity, reduced algal turbidity, reduced 

chlorophyll a, and reduced nutrients. Biological assessment data showed a return of 

expected submerged aquatic vegetation and an improved invertebrate community (rating 

as a fair quality aquatic community). This information documented the improved 

condition and helped the State define the existing use (much improved from the limited 

warmwater aquatic life designated use). However, the fish community still lacked a 

variety of species expected for this type of lake and water quality still did not meet the 

criteria for the state's designated warmwater aquatic life use. 

In response to the improved conditions, the identified existing use, and the remaining 

stressors, the State conducted a use attainability analysis (UAA) in 2005 to determine the 

highest attainable use that should be designated. The UAA demonstrated that 

implementing a stormwater management program would likely result in attainment of the 

warmwater aquatic life designated use, although it would take several years. The State 

expects the projected improved water quality levels to support a good quality aquatic 

community. Despite the number of years it might take to see improvements, the State 

determined that a warmwater aquatic life use (and not a limited warmwater aquatic life 

use) was the appropriate long term objective and revised its water quality standards to 

adopt the new designated use. 

Although it is important to recognize that the regulatory roles and requirements for 

existing and designated uses differ, decisions about each are not made in isolation. In this 

example, the aquatic community assessments not only helped to identify improvements in 

the existing condition but also helped to identify the stressors limiting attainment of a 

higher use. Information about the limiting stressors, then, was used to evaluate whether or 

not the expected condition would be attainable. As illustrated here, there is a link between 

existing and designated uses, and information about the existing condition can be used to 

inform attainability decisions. 

5) Can a state or tribe adopt the existing use as its designated use? 

In 1998, EPA stated that "Designated uses focus on the attainable condition while 

existing uses focus on the past or present condition." EPA's regulations at 40 C.F .R. § 131.10 

links these uses in a manner which intends to ensure that States and Tribes designate 

appropriate water uses, reflecting both the exiting and attainable uses of each waterbody. 18 A 

state or tribe may adopt an existing use as the designated use where it is the highest attainable 

use. However, where it is not, states and tribes must consider designating uses based on the 

18 1998 Advance Notice of Proposed Rulemaking on the Water Quality Standards Regulation. 63 FR 36,742, 36, 

748 (col. 3) (July 8, 1998). 
potential of a waterbody to attain a use, and not simply base the use designation on what has 

been attained, (i.e. the existing use). 19 

19 40 C.F.R.§§ 13 1.2and 131.10.