Maine Code § 38-465

Standards for classification of fresh surface waters
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The department shall have 4 standards for the classification of fresh surface waters which are not
classified as great ponds. [PL 1989, c. 890, Pt. A, §40 (AFF); PL 1989, c. 890, Pt. B, §61 (AMD).]
1. Class AA waters. Class AA shall be the highest classification and shall be applied to waters
which are outstanding natural resources and which should be preserved because of their ecological,
social, scenic or recreational importance.
A. Class AA waters must be of such quality that they are suitable for the designated uses of drinking
water after disinfection, fishing, agriculture, recreation in and on the water, navigation and as
habitat for fish and other aquatic life. The habitat must be characterized as free-flowing and natural.
[PL 2003, c. 227, §1 (AMD); PL 2003, c. 227, §9 (AFF); PL 2005, c. 561, §10 (AFF).]
B. The aquatic life, dissolved oxygen and bacteria content of Class AA waters must be as naturally
occurs, except that the number of Escherichia coli bacteria in these waters may not exceed a
geometric mean of 64 CFU or MPN per 100 milliliters over a 90-day interval or 236 CFU or MPN
per 100 milliliters in more than 10% of the samples in any 90-day interval. [PL 2021, c. 551, §9
(AMD).]
C. Except as provided in this paragraph, there may be no direct discharge of pollutants to Class
AA waters.
(1) Storm water discharges that are in compliance with state and local requirements are allowed
if one or more of the following conditions are met:
(a) The storm water discharge existed prior to the waters' being classified as Class AA
with a designation as an outstanding national resource as described in section 464,
subsection 4, paragraph F, subparagraph (2), including storm water discharges that existed
prior to designation of the waters as an outstanding national resource and are not licensed
by the department or were not relicensed for some duration after the waters' designation as

an outstanding national resource. This division does not authorize new or increased storm
water discharge;
(b) For storm water discharges requiring a general permit for construction, the discharge
is temporary and short term and does not permanently degrade water quality. For the
purposes of this division, a discharge is temporary and short term if the discharge occurs
only during the time necessary to construct a facility to make it operational. Best
management practices must be used during such construction; or
(c) The Class AA water is not designated as an outstanding national resource as described
in section 464, subsection 4, paragraph F, subparagraph (2) and sections 467 and 468.
(2) A discharge to Class AA waters that are or once were populated by a distinct population
segment of Atlantic salmon as determined pursuant to the United States Endangered Species
Act of 1973, Public Law 93-205, as amended, is allowed if, in addition to satisfying all the
requirements of this article, the applicant, prior to issuance of a discharge license, objectively
demonstrates to the department's satisfaction that the discharge is necessary, that there are no
other reasonable alternatives available and that the discharged effluent is for the purpose of and
will assist in the restoration of Atlantic salmon and will return the waters to a state that is closer
to historically natural chemical quality.
(3) Aquatic pesticide or chemical discharges approved by the department and conducted by
the department, the Department of Inland Fisheries and Wildlife or an agent of either agency
for the purpose of restoring biological communities affected by an invasive species are allowed.
(4) Discharges of aquatic pesticides approved by the department for the control of mosquito-
borne diseases in the interest of public health and safety using materials and methods that
provide for protection of nontarget species are allowed. When the department issues a license
for the discharge of aquatic pesticides authorized under this subparagraph, the department shall
notify the municipality in which the application is licensed to occur and post the notice on the
department's publicly accessible website.
(5) Discharges of pesticides approved by the department are allowed that are:
(a) Unintended and an incidental result of the spraying of pesticides;
(b) Applied in compliance with federal labeling restrictions; and
(c) Applied in compliance with statute, Board of Pesticides Control rules and best
management practices. [PL 2021, c. 503, §2 (AMD).]
[PL 2021, c. 503, §2 (AMD); PL 2021, c. 551, §9 (AMD).]
2. Class A waters. Class A shall be the 2nd highest classification.
A. Class A waters must be of such quality that they are suitable for the designated uses of drinking
water after disinfection; fishing; agriculture; recreation in and on the water; industrial process and
cooling water supply; hydroelectric power generation, except as prohibited under Title 12, section
403; navigation; and as habitat for fish and other aquatic life. The habitat must be characterized as
natural. [PL 2003, c. 227, §2 (AMD); PL 2003, c. 227, §9 (AFF); PL 2005, c. 561, §10
(AFF).]
B. The dissolved oxygen content of Class A waters may not be less than 7 parts per million or 75%
of saturation, whichever is higher, except that for the period from October 1st to May 14th, in order
to ensure spawning and egg incubation of indigenous fish species, the 7-day mean dissolved oxygen
concentration may not be less than 9.5 parts per million and the one-day minimum dissolved
oxygen concentration may not be less than 8.0 parts per million in identified fish spawning areas.
The aquatic life and bacteria content of Class A waters must be as naturally occurs, except that the
numbers of Escherichia coli bacteria in these waters may not exceed a geometric mean of 64 CFU

or MPN per 100 milliliters over a 90-day interval or 236 CFU or MPN per 100 milliliters in more
than 10% of the samples in any 90-day interval. [PL 2021, c. 551, §10 (AMD).]
C. Except as provided in this paragraph, direct discharges to these waters licensed after January 1,
1986 are permitted only if, in addition to satisfying all the requirements of this article, the
discharged effluent will be equal to or better than the existing water quality of the receiving waters.
Prior to issuing a discharge license, the department shall require the applicant to objectively
demonstrate to the department's satisfaction that the discharge is necessary and that there are no
other reasonable alternatives available. Discharges into waters of this classification licensed prior
to January 1, 1986 are allowed to continue only until practical alternatives exist.
(1) This paragraph does not apply to a discharge of storm water that is in compliance with state
and local requirements.
(2) This paragraph does not apply to a discharge to Class A waters that are or once were
populated by a distinct population segment of Atlantic salmon as determined pursuant to the
United States Endangered Species Act of 1973, Public Law 93-205, as amended, if, in addition
to satisfying all the requirements of this article, the applicant, prior to issuance of a discharge
license, objectively demonstrates to the department's satisfaction that the discharge is
necessary, that there are no other reasonable alternatives available and that the discharged
effluent is for the purpose of and will assist in the restoration of Atlantic salmon and will return
the waters to a state that is closer to historically natural chemical quality.
(3) This paragraph does not apply to aquatic pesticide or chemical discharges approved by the
department and conducted by the department, the Department of Inland Fisheries and Wildlife
or an agent of either agency for the purpose of restoring biological communities affected by an
invasive species.
(4) For the purpose of allowing the discharge of aquatic pesticides approved by the department
for the control of mosquito-borne diseases in the interest of public health and safety, the
department may find that the discharged effluent will be equal to or better than the existing
water quality of the receiving waters as long as the materials and methods used provide
protection for nontarget species. When the department issues a license for the discharge of
aquatic pesticides authorized under this subparagraph, the department shall notify the
municipality in which the application is licensed to occur and post the notice on the
department's publicly accessible website.
(5) This paragraph does not apply to discharges of pesticides approved by the department that
are:
(a) Unintended and an incidental result of the spraying of pesticides;
(b) Applied in compliance with federal labeling restrictions; and
(c) Applied in compliance with statute, Board of Pesticides Control rules and best
management practices. [PL 2021, c. 50, §§3, 4 (AMD).]
D. Storm water discharges to Class A waters must be in compliance with state and local
requirements. [PL 2003, c. 318, §4 (NEW).]
E. Material may not be deposited on the banks of Class A waters in any manner that makes transfer
of pollutants into the waters likely. [PL 2003, c. 318, §4 (NEW).]
[PL 2021, c. 551, §10 (AMD).]
3. Class B waters. Class B shall be the 3rd highest classification.
A. Class B waters must be of such quality that they are suitable for the designated uses of drinking
water supply after treatment; fishing; agriculture; recreation in and on the water; industrial process
and cooling water supply; hydroelectric power generation, except as prohibited under Title 12,

section 403; navigation; and as habitat for fish and other aquatic life. The habitat must be
characterized as unimpaired. [PL 2003, c. 227, §3 (AMD); PL 2003, c. 227, §9 (AFF); PL
2005, c. 561, §10 (AFF).]
B. Class B waters must be of sufficient quality to support all aquatic species indigenous to those
waters without detrimental changes in the resident biological community. The dissolved oxygen
content of Class B waters may not be less than 7 parts per million or 75% of saturation, whichever
is higher, except that for the period from October 1st to May 14th, in order to ensure spawning and
egg incubation of indigenous fish species, the 7-day mean dissolved oxygen concentration may not
be less than 9.5 parts per million and the one-day minimum dissolved oxygen concentration may
not be less than 8.0 parts per million in identified fish spawning areas. Between April 15th and
October 31st, the number of Escherichia coli bacteria in these waters may not exceed a geometric
mean of 64 CFU or MPN per 100 milliliters over a 90-day interval or 236 CFU or MPN per 100
milliliters in more than 10% of the samples in any 90-day interval. [PL 2021, c. 551, §11 (AMD).]
C. Discharges to Class B waters may not cause adverse impact to aquatic life in that the receiving
waters must be of sufficient quality to support all aquatic species indigenous to the receiving water
without detrimental changes in the resident biological community.
(1-A) For the purpose of allowing the discharge of aquatic pesticides or chemicals approved
by the department and conducted by the department, the Department of Inland Fisheries and
Wildlife or an agent of either agency to restore resident biological communities affected by an
invasive species, the department may find that the discharged effluent will not cause adverse
impact to aquatic life as long as the materials and methods used do not cause a significant loss
of any nontarget species and allow restoration of nontarget species. The department may find
that an unavoidable, temporary loss of nontarget species does not constitute a significant loss
of nontarget species.
(2) For the purpose of allowing the discharge of aquatic pesticides approved by the department
for the control of mosquito-borne diseases in the interest of public health and safety, the
department may find that the discharged effluent will not cause adverse impact to aquatic life
as long as the materials and methods used provide protection for nontarget species. When the
department issues a license for the discharge of aquatic pesticides authorized under this
subparagraph, the department shall notify the municipality in which the application is licensed
to occur and post the notice on the department's publicly accessible website. [PL 2017, c.
319, §7 (AMD).]
[PL 2021, c. 551, §11 (AMD).]
4. Class C waters. Class C shall be the 4th highest classification.
A. Class C waters must be of such quality that they are suitable for the designated uses of drinking
water supply after treatment; fishing; agriculture; recreation in and on the water; industrial process
and cooling water supply; hydroelectric power generation, except as prohibited under Title 12,
section 403; navigation; and as a habitat for fish and other aquatic life. [PL 2003, c. 227, §4
(AMD); PL 2003, c. 227, §9 (AFF); PL 2005, c. 561, §10 (AFF).]
B. Class C waters must be of sufficient quality to support all species of fish indigenous to those
waters and to maintain the structure and function of the resident biological community. The
dissolved oxygen content of Class C water may not be less than 5 parts per million or 60% of
saturation, whichever is higher, except that in identified salmonid spawning areas where water
quality is sufficient to ensure spawning, egg incubation and survival of early life stages, that water
quality sufficient for these purposes must be maintained. In order to provide additional protection
for the growth of indigenous fish, the following standards apply.

(1) The 30-day average dissolved oxygen criterion of a Class C water is 6.5 parts per million
using a temperature of 22 degrees centigrade or the ambient temperature of the water body,
whichever is less, if:
(a) A license or water quality certificate other than a general permit was issued prior to
March 16, 2004 for the Class C water and was not based on a 6.5 parts per million 30-day
average dissolved oxygen criterion; or
(b) A discharge or a hydropower project was in existence on March 16, 2005 and required
but did not have a license or water quality certificate other than a general permit for the
Class C water.
This criterion for the water body applies to licenses and water quality certificates issued on or
after March 16, 2004.
(2) In Class C waters not governed by subparagraph (1), dissolved oxygen may not be less
than 6.5 parts per million as a 30-day average based upon a temperature of 24 degrees
centigrade or the ambient temperature of the water body, whichever is less. This criterion for
the water body applies to licenses and water quality certificates issued on or after March 16,
2004.
The department may negotiate and enter into agreements with licensees and water quality certificate
holders in order to provide further protection for the growth of indigenous fish. Agreements entered
into under this paragraph are enforceable as department orders according to the provisions of
sections 347-A to 349.
Between April 15th and October 31st, the number of Escherichia coli bacteria in Class C waters
may not exceed a geometric mean of 100 CFU or MPN per 100 milliliters over a 90-day interval
or 236 CFU or MPN per 100 milliliters in more than 10% of the samples in any 90-day interval.
The board shall adopt rules governing the procedure for designation of spawning areas. Those rules
must include provision for periodic review of designated spawning areas and consultation with
affected persons prior to designation of a stretch of water as a spawning area. [PL 2021, c. 551,
§12 (AMD).]
C. Discharges to Class C waters may cause some changes to aquatic life, except that the receiving
waters must be of sufficient quality to support all species of fish indigenous to the receiving waters
and maintain the structure and function of the resident biological community. For the purpose of
allowing the discharge of aquatic pesticides or chemicals approved by the department and
conducted by the department, the Department of Inland Fisheries and Wildlife or an agent of either
agency to restore biological communities affected by an invasive species, the department may find
that the discharged effluent will not cause unacceptable changes to aquatic life as long as the
materials and methods used will ensure the support of all species of indigenous fish and the
structure and function of the resident biological community and will allow restoration of nontarget
species. [PL 2017, c. 319, §9 (AMD).]
[PL 2021, c. 551, §12 (AMD).]

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