<PAGE>
                                                                    EXHIBIT 4(a)



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                                  ALLETE, INC.
                    (formerly Minnesota Power & Light Company
                       and formerly Minnesota Power, Inc.)

                                       TO

                              THE BANK OF NEW YORK
                         (formerly Irving Trust Company)

                                       AND

                               DOUGLAS J. MACINNES

                  (successor to Richard H. West, J. A. Austin,
          E. J. McCabe, D. W. May, J. A. Vaughan and W. T. Cunningham)


                                 As Trustees under ALLETE, Inc.'s Mortgage
                                 and Deed of Trust dated as of September 1, 1945



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                       Twenty-third Supplemental Indenture
                        Providing among other things for
                First Mortgage Bonds, Pollution Control Series F
                              (Twenty-ninth Series)
                           Dated as of August 1, 2004



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<PAGE>

                       TWENTY-THIRD SUPPLEMENTAL INDENTURE

     THIS  INDENTURE,  dated as of August 1, 2004, by and between  ALLETE,  INC.
(formerly Minnesota Power & Light Company and formerly Minnesota Power, Inc.), a
corporation  of the State of  Minnesota,  whose post  office  address is 30 West
Superior  Street,  Duluth,  Minnesota 55802  (hereinafter  sometimes  called the
"Company"),  and  THE  BANK OF NEW  YORK  (formerly  Irving  Trust  Company),  a
corporation  of the State of New York,  whose post office address is 101 Barclay
Street,  New York, New York 10286  (hereinafter  sometimes called the "Corporate
Trustee"),  and DOUGLAS J. MACINNES (successor to Richard H. West, J. A. Austin,
E. J. McCabe, D. W. May, J. A. Vaughan and W. T. Cunningham),  whose post office
address is 1784 W. McGalliard Avenue,  Hamilton,  New Jersey 08610 (said Douglas
J.  MacInnes  being  hereinafter  sometimes  called  the  "Co-Trustee"  and  the
Corporate Trustee and the Co-Trustee being hereinafter together sometimes called
the "Trustees"),  as Trustees under the Mortgage and Deed of Trust,  dated as of
September 1, 1945,  between the Company and Irving Trust  Company and Richard H.
West, as Trustees,  securing  bonds issued and to be issued as provided  therein
(hereinafter  sometimes called the  "Mortgage"),  reference to which mortgage is
hereby made,  this indenture  (hereinafter  sometimes  called the  "Twenty-third
Supplemental Indenture") being supplemental thereto:

     WHEREAS, the Mortgage was filed and recorded in various official records in
the State of Minnesota; and

     WHEREAS,  an  instrument,  dated as of October 16,  1957,  was executed and
delivered under which J. A. Austin succeeded Richard H. West as Co-Trustee under
the Mortgage,  and such  instrument  was filed and recorded in various  official
records in the State of Minnesota; and

     WHEREAS,  an  instrument,  dated as of  April 4,  1967,  was  executed  and
delivered  under which E. J. McCabe in turn succeeded J. A. Austin as Co-Trustee
under the  Mortgage,  and such  instrument  was filed and  recorded  in  various
official records in the State of Minnesota; and

     WHEREAS,  under the  Sixth  Supplemental  Indenture,  dated as of August 1,
1975, to which reference is hereinafter  made, D. W. May in turn succeeded E. J.
McCabe as Co-Trustee under the Mortgage; and

     WHEREAS,  an  instrument,  dated  as of June 25,  1984,  was  executed  and
delivered  under which J. A. Vaughan in turn  succeeded D. W. May as  Co-Trustee
under the  Mortgage,  and such  instrument  was filed and  recorded  in  various
official records in the State of Minnesota; and

     WHEREAS,  an  instrument,  dated  as of July 27,  1988,  was  executed  and
delivered  under  which W. T.  Cunningham  in turn  succeeded  J. A.  Vaughan as
Co-Trustee  under the Mortgage,  and such  instrument  was filed and recorded in
various official records in the State of Minnesota; and

     WHEREAS,  on May 12, 1998, the Company filed Amended and Restated  Articles
of Incorporation  with the Secretary of State of the State of Minnesota changing
its name from Minnesota Power & Light Company to Minnesota Power, Inc. effective
May 27, 1998; and

<PAGE>

     WHEREAS,  an  instrument,  dated as of April 15,  1999,  was  executed  and
delivered  under which Douglas J. MacInnes in turn succeeded W. T. Cunningham as
Co-Trustee  under the Mortgage,  and such  instrument  was filed and recorded in
various official records in the State of Minnesota; and

     WHEREAS, on May 8, 2001, the Company filed Amended and Restated Articles of
Incorporation with the Secretary of State of the State of Minnesota changing its
name from Minnesota Power, Inc. to ALLETE, Inc.; and

     WHEREAS, by the Mortgage the Company  covenanted,  among other things, that
it would execute and deliver such supplemental  indenture or indentures and such
further  instruments and do such further acts as might be necessary or proper to
carry out more  effectually  the purposes of the Mortgage and to make subject to
the lien of the  Mortgage any  property  thereafter  acquired and intended to be
subject to the lien thereof; and

     WHEREAS,  for  said  purposes,  among  others,  the  Company  executed  and
delivered the following indentures supplemental to the Mortgage:

             DESIGNATION                                       DATED AS OF
             -----------                                       -----------
     First Supplemental Indenture.........................     March 1, 1949
     Second Supplemental Indenture........................     July 1, 1951
     Third Supplemental Indenture.........................     March 1, 1957
     Fourth Supplemental Indenture........................     January 1, 1968
     Fifth Supplemental Indenture.........................     April 1, 1971
     Sixth Supplemental Indenture.........................     August 1, 1975
     Seventh Supplemental Indenture.......................     September 1, 1976
     Eighth Supplemental Indenture........................     September 1, 1977
     Ninth Supplemental Indenture.........................     April 1, 1978
     Tenth Supplemental Indenture.........................     August 1, 1978
     Eleventh Supplemental Indenture......................     December 1, 1982
     Twelfth Supplemental Indenture.......................     April 1, 1987
     Thirteenth Supplemental Indenture....................     March 1, 1992
     Fourteenth Supplemental Indenture....................     June 1, 1992
     Fifteenth Supplemental Indenture.....................     July 1, 1992
     Sixteenth Supplemental Indenture.....................     July 1, 1992
     Seventeenth Supplemental Indenture...................     February 1, 1993
     Eighteenth Supplemental Indenture....................     July 1, 1993
     Nineteenth Supplemental Indenture....................     February 1, 1997
     Twentieth Supplemental Indenture.....................     November 1, 1997
     Twenty-First Supplemental Indenture..................     October 1, 2000
     Twenty-Second Supplemental Indenture.................     July 1, 2003

which  supplemental  indentures  were  filed  and recorded in  various  official
records in the State of Minnesota; and

                                       2

<PAGE>

     WHEREAS,  the  Company  has  heretofore  issued,  in  accordance  with  the
provisions of the Mortgage, as heretofore supplemented,  the following series of
First Mortgage Bonds:

                                                          PRINCIPAL   PRINCIPAL
                                                           AMOUNT       AMOUNT
SERIES                                                     ISSUED    OUTSTANDING
------                                                   ----------  -----------
3-1/8% Series due 1975...............................   $ 26,000,000     None
3-1/8% Series due 1979...............................      4,000,000     None
3-5/8% Series due 1981...............................     10,000,000     None
4-3/4% Series due 1987...............................     12,000,000     None
6-1/2% Series due 1998...............................     18,000,000     None
8-1/8% Series due 2001...............................     23,000,000     None
10-1/2% Series due 2005..............................     35,000,000     None
8.70% Series due 2006................................     35,000,000     None
8.35% Series due 2007................................     50,000,000     None
9-1/4% Series due 2008...............................     50,000,000     None
Pollution Control Series A...........................    111,000,000     None
Industrial Development Series A......................      2,500,000     None
Industrial Development Series B......................      1,800,000     None
Industrial Development Series C......................      1,150,000     None
Pollution Control Series B...........................     13,500,000     None
Pollution Control Series C...........................      2,000,000     None
Pollution Control Series D...........................      3,600,000     None
7-3/4% Series due 1994...............................     55,000,000     None
7-3/8% Series due March 1, 1997......................     60,000,000     None
7-3/4% Series due June 1, 2007.......................     55,000,000     None
7-1/2% Series due August 1, 2007.....................     35,000,000 $35,000,000
Pollution Control Series E...........................    111,000,000 111,000,000
7% Series due March 1, 2008..........................     50,000,000  50,000,000
6-1/4% Series due July 1, 2003.......................     25,000,000     None
7% Series due February 15, 2007......................     60,000,000  60,000,000
6.68% Series due November 15, 2007...................     20,000,000  20,000,000
Floating Rate First Mortgage Bonds due October 20, 2003  250,000,000     None
Collateral Series A..................................    255,000,000     None

which bonds are also  hereinafter  sometimes  called bonds of the First  through
Twenty-eighth Series, respectively; and

     WHEREAS, Section 8 of the Mortgage provides that the form of each series of
bonds  (other  than the First  Series)  issued  thereunder  and of coupons to be
attached to coupon bonds of such series shall be  established  by  Resolution of
the Board of  Directors  of the  Company  and that the form of such  series,  as
established by said Board of Directors,  shall specify the descriptive  title of
the bonds and various other terms thereof,  and may also contain such provisions
not

                                       3

<PAGE>

inconsistent  with the provisions of the Mortgage as the Board of Directors may,
in its discretion,  cause to be inserted therein expressing or  referring to the
terms and conditions upon which such bonds are to be issued and/or secured under
the Mortgage; and

     WHEREAS, Section 120 of the Mortgage provides, among other things, that any
power,  privilege  or right  expressly  or  impliedly  reserved to or in any way
conferred upon the Company by any provision of the Mortgage, whether such power,
privilege  or right is in any way  restricted  or is  unrestricted,  may (to the
extent  permitted  by law) be in  whole  or in part  waived  or  surrendered  or
subjected  to any  restriction  if at the  time  unrestricted  or to  additional
restriction  if already  restricted,  and the Company may enter into any further
covenants, limitations or restrictions for the benefit of any one or more series
of bonds  issued  thereunder,  or the Company may cure any  ambiguity  contained
therein,  or in any  supplemental  indenture,  or may  establish  the  terms and
provisions  of any  series  of  bonds  (other  than  said  First  Series)  by an
instrument in writing executed and acknowledged by the Company in such manner as
would be necessary  to entitle a  conveyance  of real estate to record in all of
the states in which any property at the time subject to the lien of the Mortgage
shall be situated;

     WHEREAS,  the  Company  now  desires  to create one new series of bonds and
(pursuant  to the  provisions  of  Section  120 of the  Mortgage)  to add to its
covenants and agreements contained in the Mortgage, as heretofore  supplemented,
certain  other  covenants  and  agreements to be observed by it and to alter and
amend  in  certain  respects  the  covenants  and  provisions  contained  in the
Mortgage, as heretofore supplemented; and

     WHEREAS,  the  execution  and delivery by the Company of this  Twenty-third
Supplemental  Indenture,  and the terms of the bonds of the Twenty-ninth Series,
hereinafter  referred to, have been duly authorized by the Board of Directors of
the Company by appropriate resolutions of said Board of Directors;

     NOW, THEREFORE, THIS INDENTURE WITNESSETH:

     That the Company,  in consideration of the premises and of One Dollar to it
duly paid by the  Trustees  at or before the  ensealing  and  delivery  of these
presents, the receipt whereof is hereby acknowledged, and in further evidence of
assurance of the estate,  title and rights of the Trustees and in order  further
to secure the payment of both the principal of and interest and premium, if any,
on the  bonds  from  time to time  issued  under  the  Mortgage,  as  heretofore
supplemented, according to their tenor and effect and the performance of all the
provisions of the Mortgage (including any instruments  supplemental  thereto and
any  modification  made as in the Mortgage  provided) and of said bonds,  hereby
grants,  bargains,  sells, releases,  conveys,  assigns,  transfers,  mortgages,
pledges,  sets over and confirms (subject,  however,  to Excepted  Encumbrances)
unto THE BANK OF NEW YORK  and  DOUGLAS  J.  MACINNES,  as  Trustees  under  the
Mortgage,  and to their  successor  or  successors  in said  trust,  and to said
Trustees and their successors and assigns forever, all property,  real, personal
and mixed,  of the kind or nature  specifically  mentioned in the  Mortgage,  as
heretofore supplemented,  or of any other kind or nature acquired by the Company
after the date of the  execution  and delivery of the  Mortgage,  as  heretofore
supplemented (except any herein or in the Mortgage, as heretofore  supplemented,

                                       4

<PAGE>

expressly  excepted),  now owned or, subject to the provisions of subsection (I)
of Section 87 of the Mortgage,  hereafter  acquired by the Company (by purchase,
consolidation, merger, donation, construction, erection or in any other way) and
wheresoever situated, including (without in anywise limiting or impairing by the
enumeration  of the same the scope and intent of the foregoing or of any general
description  contained in this Twenty-third  Supplemental  Indenture) all lands,
power  sites,   flowage   rights,   water   rights,   water   locations,   water
appropriations,  ditches, flumes, reservoirs, reservoir sites, canals, raceways,
dams,  dam sites,  aqueducts,  and all other rights or means for  appropriating,
conveying,  storing and supplying water; all rights of way and roads; all plants
for the generation of electricity by steam,  water and/or other power; all power
houses,  gas plants,  street  lighting  systems,  standards and other  equipment
incidental thereto,  telephone,  radio and television systems,  air-conditioning
systems and equipment incidental thereto, water works, water systems, steam heat
and hot water plants,  substations,  lines, service and supply systems, bridges,
culverts, tracks, ice or refrigeration plants and equipment,  offices, buildings
and other structures and the equipment thereof; all machinery, engines, boilers,
dynamos,  electric, gas and other machines,  regulators,  meters,  transformers,
generators, motors, electrical, gas and mechanical appliances, conduits, cables,
water,  steam heat,  gas or other  pipes,  gas mains and pipes,  service  pipes,
fittings,  valves and connections,  pole and transmission lines, wires,  cables,
tools,  implements,  apparatus,  furniture and chattels; all municipal and other
franchises, consents or permits; all lines for the transmission and distribution
of electric current,  gas, steam heat or water for any purpose including towers,
poles,  wires,  cables,  pipes,  conduits,  ducts and all  apparatus  for use in
connection therewith; all real estate, lands, easements,  servitudes,  licenses,
permits, franchises,  privileges,  rights of way and other rights in or relating
to real  estate or the  occupancy  of the same and  (except  as herein or in the
Mortgage, as heretofore  supplemented,  expressly excepted) all the right, title
and  interest of the Company in and to all other  property of any kind or nature
appertaining  to and/or used and/or  occupied  and/or enjoyed in connection with
any  property  hereinbefore  or in the  Mortgage,  as  heretofore  supplemented,
described.

     TOGETHER WITH all and singular the tenements, hereditaments, prescriptions,
servitudes  and  appurtenances  belonging  or in  anywise  appertaining  to  the
aforesaid  property or any part  thereof,  with the  reversion  and  reversions,
remainder  and  remainders  and (subject to the  provisions of Section 57 of the
Mortgage) the tolls, rents,  revenues,  issues,  earnings,  income,  product and
profits  thereof,  and all the  estate,  right,  title  and  interest  and claim
whatsoever,  at law as well  as in  equity,  which  the  Company  now has or may
hereafter acquire in and to the aforesaid property and franchises and every part
and parcel thereof.

     IT IS HEREBY  AGREED by the  Company  that,  subject to the  provisions  of
subsection  (I) of Section 87 of the  Mortgage,  all the property,  rights,  and
franchises  acquired  by  the  Company  (by  purchase,  consolidation,   merger,
donation,  construction,  erection  or in any other way) after the date  hereof,
except any herein or in the  Mortgage,  as  heretofore  supplemented,  expressly
excepted,  shall be and are as fully  granted  and  conveyed  hereby  and by the
Mortgage  and as  fully  embraced  within  the lien  hereof  and the lien of the
Mortgage  as if such  property,  rights  and  franchises  were now  owned by the
Company and were  specifically  described herein or in the Mortgage and conveyed
hereby or thereby.

                                       5

<PAGE>

     PROVIDED  that  the  following  are not and are not  intended  to be now or
hereafter granted, bargained, sold, released, conveyed,  assigned,  transferred,
mortgaged, hypothecated,  affected, pledged, set over or confirmed hereunder and
are hereby expressly  excepted from the lien and operation of this  Twenty-third
Supplemental Indenture and from the lien and operation of the Mortgage,  namely:
(1) cash,  shares  of  stock,  bonds,  notes  and  other  obligations  and other
securities not hereafter  specifically pledged,  paid,  deposited,  delivered or
held under the  Mortgage or  covenanted  so to be; (2)  merchandise,  equipment,
apparatus,  materials  or  supplies  held  for the  purpose  of  sale  or  other
disposition in the usual course of business; fuel, oil and similar materials and
supplies  consumable in the  operation of any of the  properties of the Company;
all aircraft, rolling stock, trolley coaches, buses, motor coaches,  automobiles
and other  vehicles and materials and supplies held for the purpose of repairing
or replacing (in whole or part) any of the same; all timber,  minerals,  mineral
rights and  royalties;  (3) bills,  notes and  accounts  receivable,  judgments,
demands and choses in action, and all contracts, leases and operating agreements
not  specifically  pledged  under  the  Mortgage  or  covenanted  so to be;  the
Company's  contractual  rights or other interest in or with respect to tires not
owned by the  Company;  (4) the last day of the term of any  lease or  leasehold
which may hereafter  become  subject to the lien of the  Mortgage;  (5) electric
energy,   gas,  steam,   ice,  and  other   materials  or  products   generated,
manufactured, produced or purchased by the Company for sale, distribution or use
in the ordinary course of its business;  and (6) the Company's franchise to be a
corporation;  provided, however, that the property and rights expressly excepted
from the lien and operation of this Twenty-third Supplemental Indenture and from
the lien and  operation  of the Mortgage in the above  subdivisions  (2) and (3)
shall (to the extent  permitted by law) cease to be so excepted in the event and
as of the date that  either or both of the  Trustees  or a  receiver  or trustee
shall enter upon and take  possession of the  Mortgaged and Pledged  Property in
the manner  provided in Article XIII of the Mortgage by reason of the occurrence
of a Default as defined in Section 65 thereof.

     TO HAVE AND TO HOLD all such properties, real, personal and mixed, granted,
bargained, sold, released, conveyed, assigned, transferred,  mortgaged, pledged,
set over or  confirmed by the Company as  aforesaid,  or intended so to be, unto
the Trustees and their successors and assigns forever.

     IN TRUST  NEVERTHELESS,  for the  same  purposes  and upon the same  terms,
trusts and conditions and subject to and with the same provisos and covenants as
are set forth in the Mortgage, as supplemented,  this Twenty-third  Supplemental
Indenture being supplemental thereto.

     AND IT IS HEREBY COVENANTED by the Company that all the terms,  conditions,
provisos,  covenants and  provisions  contained in the  Mortgage,  as heretofore
supplemented,  shall affect and apply to the property hereinbefore described and
conveyed and to the estate,  rights,  obligations  and duties of the Company and
Trustees and the  beneficiaries of the trust with respect to said property,  and
to the  Trustees and their  successors  in the trust in the same manner and with
the same effect as if said property had been owned by the Company at the time of
the execution of the Mortgage, and had been specifically and at length described
in and  conveyed  to said  Trustees by the  Mortgage  as a part of the  property
therein stated to be conveyed.

                                       6

<PAGE>

     The Company further covenants and agrees to and with the Trustees and their
successors in said trust under the Mortgage as follows:

                                    ARTICLE I
                          TWENTY-NINTH SERIES OF BONDS

     SECTION  1. (I)  There  shall be a series  of bonds  designated  "Pollution
Control Series F" (herein sometimes  referred to as the "Twenty-ninth  Series"),
each of which shall bear the descriptive  title "First  Mortgage Bond",  and the
form  thereof,  established  by  Resolution  of the  Board of  Directors  of the
Company,   shall  contain  suitable  provisions  with  respect  to  the  matters
hereinafter in this Section specified. Bonds of the Twenty-ninth Series shall be
dated as in Section 10 of the Mortgage provided,  mature on the maturity date of
the  Cohasset  Bonds  (as  defined  herein)  or  upon  earlier  acceleration  or
redemption,  issued as fully  registered bonds in denominations of Five Thousand
Dollars and, at the option of the Company,  in any multiple or multiples of Five
Thousand  Dollars (the  exercise of such option to be evidenced by the execution
and delivery  thereof) and shall bear interest from August 19, 2004, at the rate
borne by the  Cohasset  Bonds,  payable when  interest on the Cohasset  Bonds is
payable,  the  principal  and  interest  on each said bond to be  payable at the
office or agency of the  Company in the  Borough of  Manhattan,  The City of New
York, in such coin or currency of the United States of America as at the time of
payment is legal tender for public and private debts.

     (II) The  bonds of the  Twenty-ninth  Series  shall  be  authenticated  and
delivered  from time to time,  upon the request of the Company to the  Corporate
Trustee,  to, and  registered in the name of, the trustee under the Indenture of
Trust,  dated as of August 1, 2004 (herein  called the "Cohasset  Indenture") of
the  City of  Cohasset,  Minnesota  (the  "City"),  in  order  to  evidence  the
obligation of the Company to repay amounts  borrowed in connection with the sale
of the bonds  from time to time  issued  under the  Cohasset  Indenture  (herein
called the "Cohasset Bonds") pursuant to the Loan Agreement,  dated as of August
19,  2004,  between  the City and the  Company  (hereinafter  called  the  "Loan
Agreement"),  together with interest thereon.  Such request of the Company shall
specify the terms and principal amount of the bonds of the  Twenty-ninth  Series
to be authenticated and delivered pursuant to such request and be accompanied by
such certificates, opinions and other documents required under the Mortgage.

     The  Company  shall  receive a credit  against its  obligation  to make any
payment of the principal of or interest on the bonds of this series,  whether at
maturity,  upon  redemption  or  otherwise,  in an  amount  equal  to,  and such
obligation  shall be  fully or  partially,  as the  case may be,  satisfied  and
discharged  to the extent of,  the  amount,  if any,  credited  pursuant  to the
Cohasset Indenture against the payment required to be made by or for the account
of the City in  respect of the  corresponding  payment  of the  principal  of or
interest on the Cohasset Bonds.

     The Corporate  Trustee may conclusively  presume that the obligation of the
Company to pay the  principal of and  interest on the bonds of the  Twenty-ninth
Series as the same shall become due and payable shall have been fully  satisfied
and discharged unless and until it shall have received a written notice from the
trustee under the Cohasset Indenture, signed by its

                                       7

<PAGE>

President,  a Vice President or a Trust Officer,  stating that the corresponding
payment of  principal  of or interest on the  Cohasset  Bonds has become due and
payable and has not been fully paid and  specifying the amount of funds required
to make such payment.

     (III) If an Event of  Default  described  in  Section  701(a) or (b) of the
Cohasset  Indenture  shall  have  occurred,  in  determining  whether or not any
payment of the principal of or interest on the bonds of the Twenty-ninth  Series
shall have been made in full,  moneys received by the trustee under the Cohasset
Indenture  from the Company shall,  to the extent of the amount  remaining to be
paid by the  Company  pursuant  to  subsection  (e) of Section  3.02 of the Loan
Agreement be deemed to have been paid under said  subsection (e) and not to have
been paid on the bonds of the Twenty-ninth Series.

     The  Corporate  Trustee may  conclusively  presume that no Event of Default
described in Section 701(a) or (b) of the Cohasset Indenture shall have occurred
unless and until it shall have received a written  notice from the trustee under
the Cohasset  Indenture,  signed by its  President,  a Vice President or a Trust
Officer stating that such an event has occurred.

     (IV) From time to time, pursuant to Section 5.04 of the Loan Agreement, the
Company may amend the terms of the bonds of the Twenty-ninth  Series in order to
evidence the amended  obligation of the Company under the Loan  Agreement.  Upon
receipt of a Company  request  specifying  the amended terms of the bonds of the
Twenty-ninth  Series and requesting the  authentication  and delivery of amended
certificates for such bonds, together with a written notice signed by an officer
of the trustee under the Cohasset  Indenture  confirming that such amended terms
comply with the requirements of Section 5.04 of the Loan Agreement,  the Trustee
shall  authenticate  and deliver such amended  certificates to the trustee under
the Cohasset  Indenture.  Upon such  delivery of the amended  certificates,  the
certificates for the corresponding  bonds of the Twenty-ninth  Series previously
held by the trustee under the Cohasset  Indenture shall be deemed  superceded by
the amended certificates and shall thereafter be deemed obsolete, null and void.
The obsolete  certificates  need not be  delivered  to the Trustee  prior to the
delivery of the amended certificates, but shall be cancelled or destroyed if and
when surrendered by the trustee under the Cohasset Indenture.

     (V) On the date that any of the Cohasset Bonds or the  Additional  Cohasset
Bonds are  required to be redeemed  pursuant to Section  301(c) of the  Cohasset
Indenture,  an equal principal amount of bonds of the Twenty-ninth  Series shall
be redeemed at such principal  amount plus accrued  interest to such  redemption
date.

     The  Corporate  Trustee may  conclusively  presume that no event shall have
occurred  which would  require the Company to redeem  bonds of the  Twenty-ninth
Series  pursuant to this  Section (V) unless and until it shall have  received a
written  notice from the trustee  under the  Cohasset  Indenture,  signed by its
President, a Vice President or a Trust Officer, stating that such an event shall
have  occurred,  specifying  the  date  thereof  and  describing  such  event in
reasonable detail.

                                       8

<PAGE>

     (VI) At the option of the registered  owner,  any bonds of the Twenty-ninth
Series,  upon surrender  thereof for cancellation at the office or agency of the
Company  in the  Borough of  Manhattan,  The City of New York,  together  with a
written instrument of transfer wherever required by the Company duly executed by
the registered owner or by his duly authorized  attorney,  shall (subject to the
provisions of Section 12 of the Mortgage) be  exchangeable  for a like aggregate
principal amount of bonds of the same series of other authorized denominations.

     Bonds of the  Twenty-ninth  Series shall not be transferable  except to any
successor  trustee  under the Cohasset  Indenture,  any such transfer to be made
(subject  to the  provisions  of  Section 12 of the  Mortgage)  at the office or
agency of the Company in the Borough of Manhattan, The City of New York.

     The Company  hereby  waives any right to make a charge for any  exchange or
transfer of bonds of the Twenty-ninth Series.

     Upon the  delivery of this  Twenty-third  Supplemental  Indenture  and upon
compliance  with the  applicable  provisions of the Mortgage,  there shall be an
initial issue of bonds of the  Twenty-ninth  Series for the aggregate  principal
amount of $111,000,000.

                                   ARTICLE II
                            MISCELLANEOUS PROVISIONS

     SECTION 2. Section 126 of the Mortgage,  as heretofore  amended,  is hereby
further amended by adding the words "and July 1, 2022" after the words "July 16,
2004."

     SECTION 3.  Subject to the  amendments  provided  for in this  Twenty-third
Supplemental  Indenture,  the  terms  defined  in the  Mortgage,  as  heretofore
supplemented,   shall,  for  all  purposes  of  this  Twenty-third  Supplemental
Indenture,   have  the  meanings  specified  in  the  Mortgage,   as  heretofore
supplemented.

     SECTION 4. The Trustees hereby accept the trusts herein declared, provided,
created  or  supplemented  and  agree to  perform  the same  upon the  terms and
conditions herein and in the Mortgage set forth and upon the following terms and
conditions:

     The Trustees shall not be  responsible  in any manner  whatsoever for or in
respect  of the  validity  or  sufficiency  of  this  Twenty-third  Supplemental
Indenture or for or in respect of the recitals  contained  herein,  all of which
recitals  are made by the Company  solely.  In general,  each and every term and
condition contained in Article XVII of the Mortgage shall apply to and form part
of this Twenty-third Supplemental Indenture with the same force and effect as if
the same were  herein  set forth in full with  such  omissions,  variations  and
insertions,  if any,  as may be  appropriate  to make  the same  conform  to the
provisions of this Twenty-third Supplemental Indenture.

     SECTION 5. Whenever in this Twenty-third  Supplemental  Indenture any party
hereto is named or  referred  to,  this  shall,  subject  to the  provisions  of
Articles XVI and XVII of the

                                       9

<PAGE>

Mortgage,  as heretofore  supplemented,  be deemed to include the  successors or
assigns of such party, and all the covenants and agreements in this Twenty-third
Supplemental  Indenture  contained by or on behalf of the  Company,  or by or on
behalf  of the  Trustees  shall,  subject  as  aforesaid,  bind and inure to the
benefit of the  respective  successors  and  assigns  of such  party  whether so
expressed or not.

     SECTION 6. Nothing in this Twenty-third  Supplemental Indenture,  expressed
or implied, is intended, or shall be construed,  to confer upon, or give to, any
person,  firm or  corporation,  other than the parties hereto and the holders of
the bonds and coupons  Outstanding  under the Mortgage,  any right,  remedy,  or
claim  under or by reason of this  Twenty-third  Supplemental  Indenture  or any
covenant,  condition,  stipulation,  promise or  agreement  hereof,  and all the
covenants,   conditions,   stipulations,   promises  and   agreements   in  this
Twenty-third  Supplemental  Indenture  contained by and on behalf of the Company
shall be for the sole and exclusive  benefit of the parties  hereto,  and of the
holders of the bonds and of the coupons Outstanding under the Mortgage.

     SECTION 7. This  Twenty-third  Supplemental  Indenture shall be executed in
several counterparts,  each of which shall be an original and all of which shall
constitute but one and the same instrument.

     SECTION 8. The Company, the mortgagor named herein, by its execution hereof
acknowledges  receipt of a full,  true and  complete  copy of this  Twenty-third
Supplemental Indenture.

                                       10

<PAGE>

     IN WITNESS  WHEREOF,  ALLETE,  Inc.  has caused  its  corporate  name to be
hereunto  affixed,  and this instrument to be signed and sealed by its President
or one of its Vice  Presidents,  and its  corporate  seal to be  attested by its
Secretary or one of its  Assistant  Secretaries  for and in its behalf,  and The
Bank of New York has caused its corporate name to be hereunto affixed,  and this
instrument  to be signed and sealed by one of its Vice  Presidents or one of its
Assistant  Vice  Presidents  and its corporate seal to be attested by one of its
Assistant  Treasurers,  one of its Vice  Presidents or one of its Assistant Vice
Presidents,  and Douglas J.  MacInnes  has hereunto set his hand and affixed his
seal, all in The City of New York, as of the day and year first above written.

                                        ALLETE, INC.

                                        By     /s/ James K. Vizanko
                                          --------------------------------------
                                               James K. Vizanko
                                               Senior Vice President and Chief
                                               Financial Officer


Attest:

/s/ Deborah A. Amberg
---------------------
Deborah A. Amberg
Vice President, General Counsel
   and Secretary


Executed, sealed and delivered by ALLETE, Inc.
in the presence of:

/s/ Dawn LaPointe
-------------------


/s/ Marsha Jones
-------------------

<PAGE>

                                        THE BANK OF NEW YORK,
                                              as Corporate Trustee

                                        By      /s/ M. Ryan
                                           -------------------------------------
                                                Ming Ryan
                                                Vice President

Attest:

By /s/ J. Salovitch-Miller
  --------------------------------------
       Julie Salovitch-Miller
       Vice President


Executed, sealed and delivered by THE BANK OF NEW
YORK and DOUGLAS J. MACINNES in the presence of:

/s/ Kisha Holder
-------------------
Kisha Holder


/s/ S. Poindexter
-------------------
Stacey Poindexter

<PAGE>

                                                 /s/ Douglas J. MacInnes
                                        ----------------------------------------
                                             DOUGLAS J. MACINNES

<PAGE>

STATE OF MINNESOTA    )
                      )  SS.:
COUNTY OF ST. LOUIS   )


     On this 11th day of August, 2004, before me, a Notary Public within and for
said County,  personally  appeared JAMES K. VIZANKO and DEBORAH A. AMBERG, to me
personally  known,  who,  being  each by me duly  sworn,  did say that  they are
respectively the Senior Vice President and Chief Financial  Officer and the Vice
President,  General  Counsel  and  Secretary  of  ALLETE,  INC.  of the State of
Minnesota,  the  corporation  named in the foregoing  instrument;  that the seal
affixed to the foregoing  instrument is the corporate seal of said  corporation;
that said  instrument  was signed and  sealed in behalf of said  corporation  by
authority  of its Board of  Directors;  and said JAMES K. VIZANKO and DEBORAH A.
AMBERG  acknowledged  said  instrument  to be the  free  act  and  deed  of said
corporation.

     Personally  came  before  me on this  11th day of  August,  2004,  JAMES K.
VIZANKO,  to me  known to be the  Senior  Vice  President  and  Chief  Financial
Officer,  and DEBORAH A. AMBERG,  to me known to be the Vice President,  General
Counsel and Secretary of the above named ALLETE, INC., the corporation described
in and which executed the foregoing instrument, and to me personally known to be
the persons who as such officers  executed the foregoing  instrument in the name
and behalf of said  corporation,  who, being by me duly sworn did depose and say
and acknowledge  that they are  respectively the Senior Vice President and Chief
Financial Officer and the Vice President,  General Counsel and Secretary of said
corporation;  that the seal affixed to said  instrument is the corporate seal of
said corporation;  and that they signed, sealed and delivered said instrument in
the  name  and on  behalf  of said  corporation  by  authority  of its  Board of
Directors and stockholders, and said JAMES K. VIZANKO and DEBORAH A. AMBERG then
and  there  acknowledged  said  instrument  to be the  free act and deed of said
corporation and that such corporation executed the same.

     On the 11th day of August, 2004, before me personally came JAMES K. VIZANKO
and DEBORAH A. AMBERG,  to me known, who, being by me duly sworn, did depose and
say that they respectively reside at 1340 Mississippi Avenue, Duluth, Minnesota,
and 1923 West Kent Road, Duluth,  Minnesota; that they are respectively the Vice
President and Chief Financial  Officer and the Vice  President,  General Counsel
and Secretary of ALLETE,  INC., one of the  corporations  described in and which
executed the above instrument; that they know the seal of said corporation; that
the seal  affixed to said  instrument  is such  corporate  seal;  that it was so
affixed by order of the Board of  Directors of said  corporation,  and that they
signed their names thereto by like order.

     GIVEN under my hand and notarial seal this 11th day of August, 2004.


                                                      /s/ Jodi M. Nash
                                                      ----------------
[NOTARY SEAL]                                           JODI M. NASH
                                                  NOTARY PUBLIC - MINNESOTA
                                             My Commission Expires Jan. 31, 2005

<PAGE>

STATE OF NEW YORK    )
                     )  SS:
COUNTY OF NEW YORK   )


     On this 17th day of August, 2004, before me, a Notary Public within and for
said County,  personally  appeared Ming Ryan and Julie  Salovitch-Miller,  to me
personally known, who, being each by me duly sworn, did say that they are each a
Vice President of THE BANK OF NEW YORK of the State of New York, the corporation
named  in the  foregoing  instrument;  that the seal  affixed  to the  foregoing
instrument is the corporate seal of said  corporation;  that said instrument was
signed and sealed in behalf of said  corporation  by  authority  of its Board of
Directors;  and said  Ming  Ryan and Julie  Salovitch-Miller  acknowledged  said
instrument to be the free act and deed of said corporation.

     Personally  came before me on this 17th day of August,  2004, Ming Ryan, to
me known to be a Vice President, and Julie Salovitch-Miller, known to me to be a
Vice  President,  of the  above  named  THE BANK OF NEW  YORK,  the  corporation
described in and which executed the foregoing  instrument,  and to me personally
known to be the persons who as such officers  executed the foregoing  instrument
in the name and  behalf of said  corporation,  who,  being by me duly  sworn did
depose  and say and  acknowledge  that  they are each a Vice  President  of said
corporation;  that the seal affixed to said  instrument is the corporate seal of
said corporation;  and that they signed, sealed and delivered said instrument in
the  name  and on  behalf  of said  corporation  by  authority  of its  Board of
Directors,  and  said  Ming  Ryan and  Julie  Salovitch-Miller  then  and  there
acknowledged said instrument to be the free act and deed of said corporation and
that such corporation executed the same.

     On the 17th day of August,  2004,  before me personally  came Ming Ryan and
Julie Salovitch-Miller, to me known, who, being by me duly sworn, did depose and
say that they  respectively  reside at 33 Hudson Street,  Jersey City, NJ 07302,
and 19 Thoreau Drive,  Manalapan,  NJ 07726; that they are each a Vice President
of THE BANK OF NEW YORK, one of the corporations described in and which executed
the above instrument; that they know the seal of said corporation; that the seal
affixed to said  instrument is such  corporate  seal;  that it was so affixed by
order of the Board of Directors of said corporation,  and that they signed their
names thereto by like order.

     GIVEN under my hand and notarial seal this 17th day of August, 2004.


                                                        /s/ Robert Hirsch
                                                     -----------------------
                                                          Robert Hirsch
                                                 Notary Public State of New York
                                                        No. 01H16076679
                                                  Qualified in Rockland County
                                                 Commission Expires July 1, 2006

<PAGE>

STATE OF NEW YORK    )
                     )  SS:
COUNTY OF NEW YORK   )


     On this 17th day of August,  2004, before me personally appeared DOUGLAS J.
MACINNES,  to me  known  to be the  person  described  in and who  executed  the
foregoing instrument, and acknowledged that he executed the same as his free act
and deed.

     Personally  came before me this 17th day of August,  2004,  the above named
DOUGLAS J.  MACINNES,  to me known to be the person who executed  the  foregoing
instrument, and acknowledged the same.

     On the 17th day of  August,  2004,  before me  personally  came  DOUGLAS J.
MACINNES,  to me  known  to be the  person  described  in and who  executed  the
foregoing instrument, and acknowledged that he executed the same.

     GIVEN under my hand and notarial seal this 17th day of August, 2004.



                                                        /s/ Robert Hirsch
                                                 -------------------------------
                                                          Robert Hirsch
                                                 Notary Public State of New York
                                                        No. 01H16076679
                                                  Qualified in Rockland County
                                                 Commission Expires July 1, 2006
<PAGE>

This  instrument  was  drafted by ALLETE, Inc., 30 West Superior Street, Duluth,
Minnesota 55802.