Document:

<PAGE>

                                                                     EXHIBIT 4.2

                                                                  CONFORMED COPY

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                               AVISTA CORPORATION

                                       TO

                                 CITIBANK, N.A.

                           As Successor Trustee under
                           Mortgage and Deed of Trust,
                            dated as of June 1, 1939

                            ------------------------

                       THIRTY-FIFTH SUPPLEMENTAL INDENTURE

          Providing among other things for a series of bonds designated
                 "First Mortgage Bonds, Collateral Series 2004A"

                            ------------------------

                          Dated as of December 1, 2004

================================================================================

<PAGE>

                       THIRTY-FIFTH SUPPLEMENTAL INDENTURE

            THIS INDENTURE, dated as of the 1st day of December 2004, between
AVISTA CORPORATION (formerly known as The Washington Water Power Company), a
corporation of the State of Washington, whose post office address is 1411 East
Mission Avenue, Spokane, Washington 99202 (the "Company"), and CITIBANK, N.A.,
formerly First National City Bank (successor by merger to First National City
Trust Company, formerly City Bank Farmers Trust Company), a national banking
association incorporated and existing under the laws of the United States of
America, whose post office address is 388 Greenwich Street, 14th Floor, New
York, New York 10013 (the "Trustee"), as Trustee under the Mortgage and Deed of
Trust, dated as of June 1, 1939 (the "Original Mortgage"), executed and
delivered by the Company to secure the payment of bonds issued or to be issued
under and in accordance with the provisions thereof, this indenture (the
"Thirty-fifth Supplemental Indenture") being supplemental to the Original
Mortgage, as heretofore supplemented and amended.

            WHEREAS pursuant to a written request of the Company made in
accordance with Section 103 of the Original Mortgage, Francis M. Pitt (then
Individual Trustee under the Mortgage, as supplemented) ceased to be a trustee
thereunder on July 23, 1969, and all of his powers as Individual Trustee have
devolved upon the Trustee and its successors alone; and

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

            WHEREAS the Company has heretofore executed and delivered, in
addition to the Original Mortgage, the indentures supplemental thereto, and has
issued the series of bonds, set forth in Exhibit A hereto (the Original
Mortgage, as supplemented and amended by the First through Thirty-fourth
Supplemental Indentures being herein sometimes called collectively, the
"Mortgage"); and

            WHEREAS the Original Mortgage and the First through Thirty-third
Supplemental Indentures have been appropriately filed or recorded in various
official records in the States of Washington, California, Idaho, Montana and
Oregon, as set forth in the First through Thirty-fourth supplemental Indentures
and the Instrument of Further Assurance, dated December 15, 2001, hereinafter
referred to; and

            WHEREAS the Thirty-fourth supplemental Indenture, dated as of May 1,
2004, is to be appropriately filed and recorded; and

            WHEREAS for the purpose of confirming or perfecting the lien of the
Mortgage on certain of its properties, the Company has heretofore executed and
delivered a Short Form Mortgage and Security Agreement, in multiple counterparts
dated as of various dates in 1992, and such instrument has been appropriately
filed or recorded in the various official records in the States of California,
Montana and Oregon; and

                                       2

<PAGE>

            WHEREAS for the purpose of confirming or perfecting the lien of the
Mortgage on certain of its properties, the Company has heretofore executed and
delivered an Instrument of Further Assurance, dated as of December 15, 2001, and
such instrument has been appropriately filed or recorded in the various official
records in the States of Washington, California, Idaho, Montana and Oregon; and

            WHEREAS in addition to the property described in the Mortgage the
Company has acquired certain other property, rights and interests in property;
and

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

            WHEREAS the Company now desires to create a new series of bonds; and

            WHEREAS the execution and delivery by the Company of this
Thirty-fifth Supplemental Indenture, and the terms of the bonds of the
Thirty-third Series, hereinafter referred to, have been duly authorized by the
Board of Directors of the Company by appropriate Resolutions of said Board of
Directors, and all things necessary to make this Thirty-fifth Supplemental
Indenture a valid, binding and legal instrument have been performed;

            NOW, THEREFORE, THIS INDENTURE WITNESSETH: That the Company, in
consideration of the premises and of other good and valuable consideration, the
receipt and sufficiency whereof are hereby acknowledged, hereby confirms the
estate, title and rights of the Trustee (including, without limitation, the lien
of the Mortgage on the property of the Company subjected thereto, whether now
owned or hereafter acquired) held as security for the payment of both the
principal of and interest and premium, if any, on the bonds from time to time
issued under the Mortgage according to their tenor and effect and the
performance of all the provisions of the Mortgage and of such bonds, and,
without limiting the generality of the foregoing, hereby

                                       3

<PAGE>

confirms the grant, bargain, sale, release, conveyance, assignment, transfer,
mortgage, pledge, setting over and confirmation unto the Trustee, contained in
the Mortgage, of all the following described properties of the Company, whether
now owned or hereafter acquired, namely:

            All of the property, real, personal and mixed, of every character
      and wheresoever situated (except any hereinafter or in the Mortgage
      expressly excepted) which the Company now owns or, subject to the
      provisions of Section 87 of the Original Mortgage, may hereafter acquire
      prior to the satisfaction and discharge of the Mortgage, as fully and
      completely as if herein or in the Mortgage specifically described, and
      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 Mortgage) all lands, real estate, easements,
      servitudes, rights of way and leasehold and other interests in real
      estate; all rights to the use or appropriation of water, flowage rights,
      water storage rights, flooding rights, and other rights in respect of or
      relating to water; all plants for the generation of electricity, power
      houses, dams, dam sites, reservoirs, flumes, raceways, diversion works,
      head works, waterways, water works, water systems, gas plants, steam heat
      plants, hot water plants, ice or refrigeration plants, stations,
      substations, offices, buildings and other works and structures and the
      equipment thereof and all improvements, extensions and additions thereto;
      all generators, machinery, engines, turbines, boilers, dynamos,
      transformers, motors, electric machines, switchboards, regulators, meters,
      electrical and mechanical appliances, conduits, cables, pipes and mains;
      all lines and systems for the transmission and distribution of electric
      current, gas, steam heat or water for any purpose; all towers, mains,
      pipes, poles, pole lines, conduits, cables, wires, switch racks,
      insulators, compressors, pumps, fittings, valves and connections; all
      motor vehicles and automobiles; all tools, implements, apparatus,
      furniture, stores, supplies and equipment; all franchises (except the
      Company's franchise to be a corporation), licenses, permits, rights,
      powers and privileges; and (except as hereinafter or in the Mortgage
      expressly excepted) all the right, title and interest of the Company in
      and to all other property of any kind or nature.

The property so conveyed or intended to be so conveyed under the Mortgage shall
include, but shall not be limited to, the property set forth in Exhibit B
hereto, the particular description of which is intended only to aid in the
identification thereof and shall not be construed as limiting the force, effect
and scope of the foregoing.

            TOGETHER WITH all and singular the tenements, hereditaments 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 Original 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.

            THE COMPANY HEREBY CONFIRMS that, subject to the provisions of
Section 87 of the Original Mortgage, all the property, rights, and franchises
acquired by the

                                       4

<PAGE>

Company after the date thereof (except any hereinbefore or hereinafter or in the
Mortgage expressly excepted) are and shall be as fully embraced within the lien
of the Mortgage as if such property, rights and franchises had been owned by the
Company at the date of the Original Mortgage and had been specifically described
therein.

            PROVIDED THAT the following were not and were not intended to be
then or now or hereafter granted, bargained, sold, released, conveyed, assigned,
transferred, mortgaged, pledged, set over or confirmed under the Mortgage and
were, are and shall be expressly excepted from the lien and operation namely:
(l) cash, shares of stock and obligations (including bonds, notes and other
securities) not hereafter specifically pledged, paid, deposited or delivered
under the Mortgage or covenanted so to be; (2) merchandise, equipment, materials
or supplies held for the purpose of sale in the usual course of business or for
consumption in the operation of any properties of the Company; (3) bills, notes
and accounts receivable, and all contracts, leases and operating agreements not
specifically pledged under the Mortgage or covenanted so to be; (4) electric
energy 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 (5) any property heretofore released pursuant to any
provisions of the Mortgage and not heretofore disposed of by the Company;
provided, however, that the property and rights expressly excepted 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 that the
Trustee or a receiver or trustee shall enter upon and take possession of the
Mortgaged and Pledged Property in the manner provided in Article XII of the
Original Mortgage by reason of the occurrence of a Completed Default as defined
in said Article XII.

            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 in the Mortgage as aforesaid, or
intended so to be, unto the Trustee, and its successors, heirs 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 set forth in the Mortgage, this Thirty-fifth Supplemental Indenture
being supplemental to the Mortgage.

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

            The Company further covenants and agrees to and with the Trustee and
its successor or successors in such trust under the Mortgage, as follows:

                                       5

<PAGE>

                                   ARTICLE I

                          THIRTY-THIRD SERIES OF BONDS

            SECTION 1. (I) There shall be a series of bonds designated
"Collateral Series 2004A" (herein sometimes referred to as the "Thirty-third
Series"), each of which shall also bear the descriptive title First Mortgage
Bond, and the form thereof, which has been established by Resolution of the
Board of Directors of the Company, is set forth on Exhibit C hereto. Bonds of
the Thirty-third Series shall be issued as fully registered bonds in
denominations of One Thousand Dollars and, at the option of the Company, any
amount in excess thereof (the exercise of such option to be evidenced by the
execution and delivery thereof) and shall be dated as in Section 10 of the
Mortgage provided. Each bond of the Thirty-third Series shall mature, be
redeemable and have such other terms and provisions as set forth below.

            (II)  The Bonds of the Thirty-third Series shall have the following
terms and characteristics:

            (a)   the Bonds of the Thirty-third Series shall be initially
      authenticated and delivered under the Mortgage in the respective principal
      amounts and shall mature on the respective dates set forth below:

<TABLE>
<CAPTION>
Aggregate Principal Amount    Stated Maturity Date
--------------------------    --------------------
<S>                           <C>
       $ 13,850,000           December 10, 2007
         25,000,000           December 10, 2007
         25,000,000           October 26, 2010
         25,000,000           June 19, 2028
       ------------
       $ 88,850,000
</TABLE>

            (b)   the Bonds of the Thirty-third Series shall not bear interest;

            (c)   the principal of each Bond of the Thirty-third Series shall be
      payable upon presentation thereof at the office or agency of the Company
      in the Borough of Manhattan, The City of New York, in such coin or
      currency as at the time of payment is legal tender for public and private
      debts;

            (d)   the Bonds of the Thirty-third Series shall be redeemable, in
      whole at any time or in part from time to time, at the option of the
      Company, at the principal amount thereof;

            (e)   (i) the Bonds of the Thirty-third Series are to be issued and
      delivered to, and held by, the Indenture Trustee for the benefit of the
      Holders of all Benefitted Securities from time to time outstanding under
      the Indenture (as such terms are hereinafter defined);

            (ii)  in the event that the Notes (as hereinafter defined) maturing
      on June 19, 2028, or any principal amount thereof, are to be redeemed on
      June 19, 2008 in

                                       6

<PAGE>

      accordance with the provisions thereof, Bonds of the Thirty-third Series
      having a stated maturity date of June 19, 2028, in the principal amount of
      the Notes so to be redeemed, shall be redeemed on June 19, 2008 at the
      principal amount thereof;

            (iii) in the event that the maturity of all outstanding Benefitted
      Securities shall have been accelerated following an Event of Default (as
      defined in the Indenture), all Outstanding Bonds of the Thirty-third
      Series shall be redeemed at the principal amount thereof (the obligation
      to effect such redemption being rescinded upon the rescission of such
      acceleration);

            (iv)  the obligation of the Company to pay the principal of Bonds of
      the Thirty-third Series of any stated maturity at or after Maturity shall
      be satisfied and discharged to the extent of the amount, if any, paid by
      the Company in respect of the corresponding amount of principal then due
      on the Notes of the same stated maturity;

            (v)   the Trustee shall be entitled to presume that the obligation
      of the Company to pay the principal of Bonds of the Thirty-third 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 Indenture Trustee, signed by an authorized officer thereof, stating
      that the principal of Bonds of the Thirty-third Series has become due and
      payable and has not been fully paid, and specifying the amount of funds
      required to make such payment;

            (f)   no service charge shall be made for the registration of
      transfer or exchange of Bonds of the Thirty-third Series;

            (g)   in the event of an application by the Indenture Trustee for a
      substituted Bond of the Thirty-third Series pursuant to Section 16 of the
      Original Mortgage, the Indenture Trustee shall not be required to provide
      any indemnity or pay any expenses or charges as contemplated in said
      Section 16; and

            (h)   the Bonds of the Thirty-third Series shall have such other
      terms as are set forth in the form of bond attached hereto as Exhibit C.

            Anything in this Supplemental Indenture or in the Bonds of the
Thirty-third Series to the contrary notwithstanding, if, at the time of the
Maturity of such Bonds of any stated maturity, the stated aggregate principal
amount of such Bonds of such stated maturity then Outstanding shall exceed the
aggregate principal amount of Notes of such stated maturity then outstanding
under the Indenture, the aggregate principal amount of such Bonds of such stated
maturity shall be deemed to have been reduced by the amount of such excess.

            (III) For all purposes of this Thirty-fifth Supplemental Indenture,
except as otherwise expressly provided or unless the context otherwise requires,
the terms defined below shall have the meanings specified:

            "BENEFITTED SECURITIES" has the meaning specified in the Indenture.

                                       7

<PAGE>

            "INDENTURE" means the Indenture, dated as of April 1, 1998, between
      the Company and JPMorgan Chase Bank, N.A. (successor to The Chase
      Manhattan Bank), as amended and supplemented by various instruments
      including without limitation the Officer's Certificate.

            "INDENTURE TRUSTEE" means the trustee under the Indenture.

            "MATURITY" means the date on which the principal of the Bonds of the
      Thirty-third Series becomes due and payable, whether at stated maturity,
      upon redemption or acceleration, or otherwise.

            "NOTES" means the Company's Medium-Term Notes, Series C, established
      by the Officer's Certificate and issued and outstanding under the
      Indenture.

            "OFFICER'S CERTIFICATE" means the Officer's Certificate, dated April
      24, 1998, executed by the Company and delivered to the Indenture Trustee.

            A copy of the Indenture is on file at the office of the Indenture
Trustee at 560 Mission Street, 13th Floor, San Francisco, CA 94105 and at the
office of the Company at 1411 East Mission Avenue, Spokane, WA 99202.

            (IV)  Upon the delivery of this Thirty-fifth Supplemental Indenture,
Bonds of the Thirty-third Series in the aggregate principal amount of
$88,850,000 are to be issued and will be Outstanding, in addition to
$783,500,000 aggregate principal amount of bonds of prior series Outstanding at
the date of delivery of this Thirty-fifth Supplemental Indenture.

                                   ARTICLE II

                              PROSPECTIVE AMENDMENT

            SECTION 1. The owners of the Bonds of the Thirty-third Series shall
be deemed to have consented to the amendment of Section 28 of the Original
Mortgage to add at the end thereof a new paragraph reading as follows:

                  Notwithstanding the foregoing, any Opinion of Counsel
            delivered pursuant to subdivision (7) of this Section 28, or
            pursuant to any other provision of this Indenture by reference to
            this Section 28, may, at the election of the Company, omit any or
            all of the statements contained in clause (a) of subdivision (7) if
            there shall have been delivered to the Trustee a policy of title
            insurance (or endorsement thereto) issued by a nationally recognized
            title insurance company, in an amount not less than twenty-eight
            percent (28%)(1) of the cost or fair value to the Company (whichever
            is less) of the Property Additions made the basis of such
            application, insuring, in customary terms, against risk of loss
            sustained or

---------------------
(1)   The owners of the Bonds of the Thirty-third Series shall be deemed to have
      consented to the amendment contained in this Section 1 of Article II,
      either with the percentage shown above or with any higher percentage.

                                       8

<PAGE>

            incurred by the Trustee by reason of any circumstances or conditions
            by virtue of which the statements omitted from clause (a) of such
            Opinion of Counsel would not have been accurate if made.

                                  ARTICLE III

                            MISCELLANEOUS PROVISIONS

            SECTION 1. The terms defined in the Original Mortgage shall, for all
purposes of this Thirty-fifth Supplemental Indenture, have the meanings
specified in the Original Mortgage.

            SECTION 2. The Trustee hereby confirms its acceptance of the trusts
in the Original Mortgage declared, provided, created or supplemented and agrees
to perform the same upon the terms and conditions in the Original Mortgage set
forth, including the following:

            The Trustee shall not be responsible in any manner whatsoever for or
in respect of the validity or sufficiency of this Thirty-fifth Supplemental
Indenture or for or in respect of the recitals contained herein, all of which
recitals are made by the Company solely. Each and every term and condition
contained in Article XVI of the Original Mortgage, shall apply to and form part
of this Thirty-fifth 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 Thirty-fifth Supplemental Indenture.

            SECTION 3. Whenever in this Thirty-fifth Supplemental Indenture
either of the parties hereto is named or referred to, this shall, subject to the
provisions of Articles XV and XVI of the Original Mortgage be deemed to include
the successors and assigns of such party, and all the covenants and agreements
in this Thirty-fifth Supplemental Indenture contained by or on behalf of the
Company, or by or on behalf of the Trustee, or either of them, shall, subject as
aforesaid, bind and inure to the respective benefits of the respective
successors and assigns of such parties, whether so expressed or not.

            SECTION 4. Nothing in this Thirty-fifth Supplemental Indenture,
expressed or implied, is intended, or shall be construed, to confer upon, or to
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 Thirty-fifth Supplemental Indenture
or any covenant, condition, stipulation, promise or agreement hereof, and all
the covenants, conditions, stipulations, promises and agreements in this
Thirty-fifth Supplemental Indenture contained by or 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 5. This Thirty-fifth 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.

                                       9

<PAGE>

            SECTION 6. The titles of the several Articles of this Thirty-fifth
Supplemental Indenture shall not be deemed to be any part thereof.

                                       10

<PAGE>

            IN WITNESS WHEREOF, on the 15th day of December, 2004, AVISTA
CORPORATION 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 Corporate Secretary or
one of its Assistant Corporate Secretaries for and in its behalf, all in The
City of Spokane, Washington, as of the day and year first above written; and on
the 15th day of December, 2004, CITIBANK, N.A., 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 or one of its Senior Trust Officers or
one of its Trust Officers and its corporate seal to be attested by one of its
Vice Presidents or one of its Trust Officers, all in The City of New York, New
York, as of the day and year first above written.

                                         AVISTA CORPORATION

                                         By: /s/ Malyn K. Malquist
                                             -----------------------------------
                                                    Senior Vice President

Attest:

  /s/ Susan Y. Miner
----------------------------------
     Assistant Corporate Secretary

Executed, sealed and delivered
  by AVISTA CORPORATION
  in the presence of:

  /s/ Diane C. Thoren
----------------------------------
     Diane C. Thoren

  /s/ Paul W. Kimball
----------------------------------
     Paul W. Kimball

                                       11

<PAGE>

                                         CITIBANK, N.A., AS TRUSTEE

                                         By: /s/ Wafaa Orfy
                                             -----------------------------------
                                                 Wafaa Orfy, Vice President

Attest:

  /s/ Nancy Forte
----------------------------------
  Nancy Forte, Assistant Vice President

Executed, sealed and delivered
  by CITIBANK, N.A.,
  as trustee. in the presence of:

         /s/ R.T. Kirchner
----------------------------------
         R.T. Kirchner
         Vice President

         /s/ John J. Byrnes
----------------------------------
         John J. Byrnes
         Vice President

                                       12

<PAGE>

STATE OF WASHINGTON    )
                       ) ss.:
COUNTY OF SPOKANE      )

            On the 15th day of December 2004, before me personally appeared
Malyn Malquist, to me known to be a Senior Vice President of AVISTA CORPORATION,
one of the corporations that executed the within and foregoing instrument, and
acknowledged said instrument to be the free and voluntary act and deed of said
Corporation for the uses and purposes therein mentioned and on oath stated that
he was authorized to execute said instrument and that the seal affixed is the
corporate seal of said Corporation.

            On the 15th day of December 2004, before me, Sue Miner, a Notary
Public in and for the State and County aforesaid, personally appeared Malyn
Malquist, known to me to be a Senior Vice President of AVISTA CORPORATION, one
of the corporations that executed the within and foregoing instrument and
acknowledged to me that such Corporation executed the same.

            IN WITNESS WHEREOF, I have hereunto set my hand and affixed my
official seal the day and year first above written.

                                          /s/ Susan Y. Miner
                                         ---------------------------------------
                                                  Notary Public

                                              Sue Miner
                                              Notary Public
                                              Commission Expires August 20, 2007
                                              State of Washington

                                       13

<PAGE>

STATE OF NEW YORK     )
                      ) ss.:
COUNTY OF NEW YORK    )

            On the 13th day of December 2004, before me personally appeared
Wafaa Orfy, to me known to be a Vice President of CITIBANK, N.A., one of the
corporations that executed the within and foregoing instrument, and acknowledged
said instrument to be the free and voluntary act and deed of said Corporation
for the uses and purposes therein mentioned and on oath stated that he was
authorized to execute said instrument and that the seal affixed is the corporate
seal of said Corporation.

            On the 13th day of December 2004, before me, a Notary Public in and
for the State and County aforesaid, personally appeared Wafaa Orfy, known to me
to be an Vice President of CITIBANK, N.A., one of the corporations that executed
the within and foregoing instrument and acknowledged to me that such Corporation
executed the same.

            IN WITNESS WHEREOF, I have hereunto set my hand and affixed my
official seal the day and year first above written.

                                          /s/ Nanette Murphy
                                         ---------------------------------------
                                                   Notary Public

                                              NANETTE MURPHY
                                              Notary Public, State of New York
                                              No. 01MU6086415
                                              Qualified in Kings County
                                              Commission Expires 1/21/07

                                       14

<PAGE>

                                                                       EXHIBIT A

                        MORTGAGE, SUPPLEMENTAL INDENTURES
                               AND SERIES OF BONDS

<TABLE>
<CAPTION>
 MORTGAGE OR                                                                 PRINCIPAL      PRINCIPAL
SUPPLEMENTAL          DATED AS                        SERIES                  AMOUNT         AMOUNT
 INDENTURE              OF            NO.           DESIGNATION               ISSUED       OUTSTANDING
-------------    -----------------    ---    --------------------------    ------------    -----------
<S>              <C>                  <C>    <C>                           <C>             <C>
Original         June 1, 1939           1      3-1/2% Series due 1964      $ 22,000,000       None

First            October 1, 1952        2      3-3/4% Series due 1982        30,000,000       None

Second           May 1, 1953            3      3-7/8% Series due 1983        10,000,000       None

Third            December 1, 1955                       None

Fourth           March 15, 1957                         None

Fifth            July 1, 1957           4      4-7/8% Series due 1987        30,000,000       None

Sixth            January 1, 1958        5      4-1/8% Series due 1988        20,000,000       None

Seventh          August 1, 1958         6      4-3/8% Series due 1988        15,000,000       None

Eighth           January 1, 1959        7      4-3/4% Series due 1989        15,000,000       None

Ninth            January 1, 1960        8      5-3/8% Series due 1990        10,000,000       None

Tenth            April 1, 1964          9      4-5/8% Series due 1994        30,000,000       None

Eleventh         March 1,1965          10      4-5/8% Series due 1995        10,000,000       None

Twelfth          May 1, 1966                            None

Thirteenth       August 1, 1966        11      6    % Series due 1996        20,000,000       None

Fourteenth       April 1, 1970         12      9-1/4% Series due 2000        20,000,000       None

Fifteenth        May 1, 1973           13      7-7/8% Series due 2003        20,000,000       None

Sixteenth        February 1, 1975      14      9-3/8% Series due 2005        25,000,000       None

Seventeenth      November 1, 1976      15      8-3/4% Series due 2006        30,000,000       None

Eighteenth       June 1, 1980                           None

Nineteenth       January 1, 1981       16     14-1/8% Series due 1991        40,000,000       None

Twentieth        August 1, 1982        17        15-3/4% Series due          60,000,000       None
                                                     1990-1992

Twenty-First     September 1, 1983     18     13-1/2% Series due 2013        60,000,000       None

Twenty-Second    March 1, 1984         19     13-1/4% Series due 1994        60,000,000       None

Twenty-Third     December 1, 1986      20      9-1/4% Series due 2016        80,000,000       None

Twenty-Fourth    January 1, 1988       21     10-3/8% Series due 2018        50,000,000       None

Twenty-Fifth     October 1, 1989       22      7-1/8% Series due 2013        66,700,000       None

                                       23      7-2/5% Series due 2016        17,000,000       None

Twenty-Sixth     April 1, 1993         24    Secured Medium-Term Notes,     250,000,000    89,500,000
                                               Series A($250,000,000
                                                    authorized)

Twenty-Seventh   January 1, 1994       25    Secured Medium-Term Notes,     161,000,000    59,000,000
                                               Series B ($250,000,000
                                                    authorized)

Twenty-Eighth    September 1, 2001     26    Collateral Series due 2002     220,000,000       None

Twenty-Ninth     December 1, 2001      27      7.75% Series due 2007        150,000,000    150,000,000

Thirtieth        May 1, 2002           28    Collateral Series due 2003     225,000,000       None

Thirty-First     May 1, 2003           29    Collateral Series due 2004     245,000,000       None

Thirty-Second    September 1, 2003     30      6.125% Series due 2013        45,000,000     45,000,000

Thirty-Third     May 1, 2004           31    Collateral Series due 2005     350,000,000    350,000,000

Thirty-fourth    November 1, 2004      32      5.45% Series due 2019         90,000,000     90,000,000
</TABLE>

                                      A-1

<PAGE>

                                                                       EXHIBIT B

                               PROPERTY ADDITIONS

      (A)   Miscellaneous Fee-Owned Real Estate in the States of Washington and
Idaho:

PARCEL 1

The West Half of the Northwest Quarter of the Southwest Quarter (W 1/2 NW 1/4
SW 1/4) of Section 11, Township 57 NORTH, Range 1 East, Boise Meridian, Bonner
County, Idaho.

PARCEL 2

The East Half of the Northwest Quarter of the Southwest Quarter (E 1/2 NW 1/4
SW 1/4) of Section 11, Township 57 NORTH, Range 1 East, Boise Meridian, Bonner
County, Idaho.

PARCEL 3

A parcel of land lying in a portion of the South Half (S 1/2) of Section 11,
Township 57 North, Range 1 East, BoisE Meridian, Bonner County, Idaho, more
particularly described as follows:

Commencing at the center quarter corner of said Section 11, a found 3 1/4"
aluminum cap, monumenting said corner, which bears North 00(degrees)00'02" East,
2631.61 feet from the South quarter corner of said Section 11, a found 3 1/4"
aluminum cap, monumenting said corner;

thence South 89(degrees)51'30" West, 452.96 feet, along the East-West centerline
of said Section 11, to the Point of Beginning;

thence continuing South 89(degrees)51'30" West, 878.15 feet to the Center-West
1/16th corner;

thence South 00(degrees)02'51" East, 1689.29 feet along the North-South West
1/16th line to a point in the centerline oF an existing 40 foot wide road
easement (Trestle Creek Road);

thence Northeasterly along said existing road centerline the following two (2)
courses:

1.    Northeasterly along a 1000.00 foot radius curve right (the chord of which
bears North 54(degrees)43'32" East, 182.81 feet) through a central angle of
10(degrees)29'20", an arc distance of 183.06 feet;

2.    North 59(degrees)58'12" East, 142.21 feet;

thence leaving said existing road centerline, South 21(degrees)31'11" East,
107.59 feet;

thence South 32(degrees)15'27" East, 40 feet, more or less, to the thread of
Trestle Creek;

thence Northeasterly along said thread of Trestle Creek, 612 feet, more or less,
to a point in a line which bears South from the Point of Beginning;

<PAGE>

thence leaving said thread of Trestle Creek, North 1408 feet, more or less, to
the Point of Beginning.

TOGETHER WITH AND SUBJECT TO a 10 foot wide utility easement lying on each side,
parallel with and adjoining to the existing 40 foot wide ingress and egress road
easement (Trestle Creek Road)

PARCEL 4

A tract of land located in a portion of Section 11, Township 57 North, Range 1
East of the Boise Meridian, Bonner County, Idaho, more particularly described as
follows:

Commencing at the Southwest corner of said Section 11;

thence North along the West line of Section 11, a distance of 204.00 feet to
corner number 2 of that parcel of land described in Instrument No. 86437,
records of Bonner County, Idaho, said point being the True Point of Beginning;

thence continuing North along said West line of Section 11, a distance of 76.83
feet;

thence North 82(degrees)19'15" East, a distance of 87.33 feet;

thence South 24(degrees)42'57" East, a distance of 119.65 feet;

thence South 31(degrees)13'40" West, a distance of 128.42 feet to corner number
4 of said parcel;

thence North a distance of 130.00 feet to corner number 3 of said parcel;

thence West, a distance of 70.00 feet to the True Point of Beginning.

LESS the Forest Service Road right of way.

PARCEL 5

A parcel of land in Government Lot 9, Section 10, Township 57 North, Range 1
East, Boise Meridian, Bonner County, Idaho, described as follows:

Beginning at the position of the Section corner common to Sections 10, 11, 14
and 15, from which a Reference Monument (brass cap on an iron pipe) bears North
12(degrees)55'31" East, 15.51 feet;

thence North 0(degrees)03'30" West along the Section line common to Sections 10
and 11, 201.39 feet to corner 1 and the True Point of Beginning, a 3/4" x 30"
rebar with a Standard Forest Service Aluminum Cap, marked USDA-FS S10 COR 1 STA
ID 150 PLS 4343 1994;

thence North 0(degrees)03'30" West along the same line, 79.44 feet to corner 2,
a 3/4" x 30" rebar with a Standard ForesT Service Aluminum Cap, marked USDA-FS
S10 COR 2 STA ID 150 PLS 4343 1994;

                                      B-2

<PAGE>

thence South 89(degrees)20'08" West, 70.99 feet to corner 3, a 3/4" x 30" rebar
with a Standard Forest Service Aluminum Cap marked USDA-FS S10 COR 3 STA ID 150
PLS 4343 1994;

thence South 28(degrees)30'27" East, 104.93 feet to corner 4, a 3/4" x 30" rebar
with a Standard Forest Service Aluminum Cap marked USDA-FS S10 COR 4 STA ID 150
PLS 4343 1994;

thence North 57(degrees)04'14" East, 25.00 feet to corner 1 and the True Point
of Beginning.

PARCEL 6

The Southwest Quarter of the Southeast Quarter (SW 1/4 SE 1/4) of Section 3,
Township 53 North, Range 1 West, Boise Meridian, Bonner County, Idaho.

EXCEPT a tract of land in the Southwest Quarter of the Southeast Quarter (SW 1/4
SE 1/4) of said Section 3, more fulLy described as follows:

Beginning at the South quarter corner of said Section 3, thence North
89(degrees)52'50" East, 145.3 feet:

thence North 31(degrees)43'20" East, 1546.6 feet;

thence South 8(degrees)00'40" East, 149.7 feet to the True Point of Beginning;

thence South 81(degrees)59'20" West, 10.0 feet;

thence South 31(degrees)12'20" West, 44.3 feet;

thence South 8(degrees)00'40" East, 215.7 feet;

thence North 81(degrees)59'20" East, 100.00 feet;

thence North 8(degrees)00'40" West, 250.0 feet;

thence South 81(degrees)59'20" West, 62.0 feet, more or less, to the True Point
of Beginning;

ALSO EXCEPT a tract Beginning at the Southeast corner of the Southwest quarter
of the Southeast quarter (SW 1/4 SE 1/4) of Section 3, Township 53 North, Range
1 West, Boise Meridian, Bonner County, Idaho;

thence North along the East line of said 1/16th section, a distance of 1060
feet;

thence West to the center of South Gold Creek;

thence Southerly along the centerline of said creek to the South line of said
1/16th section;

thence East along the South line of said 1/16th section to the Point of
Beginning;

                                       B-3

<PAGE>

ALSO EXCEPT commencing at the Southwest corner of the Southwest Quarter of the
Southeast Quarter (SW 1/4 SE 1/4) of Section 3, Township 53 North, Range 1 West,
Boise Meridian, Bonner County, Idaho;

thence North along the West line of said 1/16th section a distance of 860 feet;

thence East to the center of South Gold Creek:

thence Southerly along the centerline of said South Gold Creek to the South line
of said 1/16th section;

thence West along the South line of said 1/16th section to the Point of
Beginning.

ALSO EXCEPT an "L" shaped portion of land in Section 3, Township 53 North, Range
1 West, Boise Meridian, Bonner County, Idaho, generally located in the Southeast
corner of Lot 5, and the Northeast corner of the Southeast Quarter of the
Southwest Quarter (SE 1/4 SW 1/4);

And the Northwest corner of the Southwest Quarter of the Southeast Quarter
(SW 1/4 SE 1/4) more fully described as follows:

Beginning at that point at which the South end of the East boundary line of Lot
5 meets the West end of the North boundary line of the Southwest Quarter of the
Southeast Quarter (SW 1/4 SE 1/4) and proceeding North along said East line of
Lot 5 for a distance of 310 feet;

thence West at a right angle from said East line of Lot 5 for a distance of 188
feet;

thence South parallel with the East line of Lot 5 and with the Northerly portion
of the West boundary line of the Southwest Quarter of the Southeast Quarter (SW
1/4 SE 1/4) for a distance of 370 feet; the last 60 feet approximatelY of said
line being located in the Southeast Quarter of said Southwest Quarter (SE 1/4 SW
1/4);

thence East parallel with the South line of Lot 5 and the North line of the
Southwest Quarter or the Southeast Quarter (SW 1/4 SE 1/4) to the midpoint of
South Gold Creek a distance of approximately 650 feet;

thence North along the midpoint line of the bed of South Gold Creek to the North
boundary line of the Southwest Quarter of the Southeast Quarter (SW 1/4 SE 1/4);

thence West along the North boundary line of the Southwest Quarter of the
Southeast Quarter (SW 1/4 SE 1/4) to the TRue Point of Beginning, the juncture
of the South end of the East boundary line of Lot 5 and the West end of the
North boundary line of the Southwest Quarter of the Southeast Quarter (SW 1/4 SE
1/4).

PARCEL 7

                                      B-4

<PAGE>

Commencing at the Southeast corner of the Northwest Quarter of the Northeast
Quarter (NW 1/4 NE 1/4) of Section 10, Township 53 North, Range 1 West, Boise
Meridian, Bonner County, Idaho;

thence North along the East line of said 1/16th section a distance of 1320 feet,
more or less, to the Northeast corner of said 1/16th section;

thence West along the North line of said 1/16th section to the center of South
Gold Creek;

thence Southerly along the center line of said creek to the South line of said
1/16th section;

thence East along the South line of said 1/16th section to the Point of
Beginning.

PARCEL 8

A triangular shaped parcel of land being a portion of Government Lot 5, Section
3, Township 53 North, Range 1 West, Boise Meridian, Bonner County, Idaho and
being described as follows:

Commencing at the Southeast corner of Government Lot 5;

thence North along the East line thereof 1435 feet, more or less, to a point on
the Southwesterly line of the plat of Lakeview according to the plat thereof,
recorded in Book "B" of Plats, page 59, records of Bonner County, Idaho;

thence North 69(degrees)07'00" West, 764 feet, more or less, to an aluminum pipe
and cap on the Southeast line of North Gold Creek Lime Placer Survey No. 762;

thence parallel to the West line of Government Lot 5, South 00(degrees)15'29"
West, a distance of 588.01 feet to a found iron rod and PLS 4194 cap;

thence parallel to the South line of Government Lot 5, South 89(degrees)50'40"
East, a distance of 111.91 feet to the Point of Beginning;

thence continuing along a line parallel to the South line of Government Lot 5,
South 89(degrees)50'40" East, a distance of 111.91 feet to a found iron rod and
PLS 4194 cap;

thence along a line parallel to the West line of Government Lot 5, South
00(degrees)15'29" West, a distance of 111.91 feet;

thence North 44(degrees)47'35" West, a distance of 158.13 feet to the Point of
Beginning.

AND a portion of Government Lot 5, Section 3, Township 53 North, Range 1 West,
Boise Meridian, Bonner County, Idaho, more fully described as follows:

Beginning at the Southeast corner of Government Lot 5;

thence North 310 feet along the East line of said Government Lot to the True
Point of Beginning;

                                      B-5

<PAGE>

thence North along said East line 1125 feet, more or less, to a point on the
Southwest line of the plat of Lakeview;

thence North 69(degrees)07'00" West, 764 feet, more or less, to a point on the
Southeast line of North Gold Creek Lime Placer Survey #762;

thence South 54(degrees)30'00" West, 200.6 feet to the Southeast corner of South
Gold Creek Lime Placer Survey #761;

thence South 69(degrees)38'00" West along the Southeast line of Survey #761, a
distance of 227 feet;

thence South, parallel to the West line of Government Lot 5, a distance of 392
feet;

thence West, parallel to the South line of Government Lot 5, a distance of 130
feet, more or less, to a point which is 100 feet East of the West line of said
Government Lot;

thence South, parallel to the West line of said Government Lot, 560 feet;

thence South 45(degrees)00'00" East, 792 feet, more or less, to a point on the
South line of said Government Lot;

thence East along said South line 472 feet, more or less, to a point which is
188 feet West of the Southeast corner of Government Lot 5;

thence North, parallel to the East line of said Government Lot, 310 feet;

thence East 188 feet to the True Point of Beginning.

EXCEPT that portion of Government Lot 5 in Section 3, Township 53 North, Range 1
West, Boise Meridian, Bonner County, Idaho, described as follows:

Beginning at the Southeast corner of said Lot 5;

Thence North along the East line thereof 1435 feet, more or less, to a point on
the Southwesterly line of the plat of Lakeview, according to the plat thereof,
recorded in Book 1 of Plats, Page 44, records of Bonner County, Idaho;

Thence North 69(degrees)07'00" West, 764 feet, more or less, to a point on the
Southeast line of North Gold Creek Lime Placer Survey No. 762, said point being
the True Point of Beginning;

thence South 54(degrees)30'00" West, 200.6 feet to the Southeast corner of South
Gold Creek Lime Placer Survey #761;

thence South 69(degrees)38'00" West along the Southeast line of said Survey No.
761, a distance of 227 feet;

thence South, parallel to the West line of said Government Lot 5, a distance of
392 feet;

                                      B-6

<PAGE>

thence West, parallel to the South line of said Lot 5, a distance of 130 feet,
more or less, to a point hereinafter referred to as Point A, that is 100 feet
East of the West line of said Lot 5;

thence South, parallel to said West line, 560 feet;

thence South 45(degrees)00'00" East, 792 feet, more or less, to a point on the
South line of said Lot 5;

thence East along said South line 172 feet;

thence North, parallel to the West line of said Lot 5, a distance of 1120 feet,
more or less, to a point in a line running through said Point A, that is
parallel with the South line of said Government Lot 5;

thence West, 240 feet, more or less, to a point in a line running through the
True Point of Beginning, that is parallel with the West line of said Government
Lot 5;

thence North along said line 590 feet, more or less, to the True Point of
Beginning.

ALSO EXCEPTING a triangular shaped parcel of land being a portion of Government
Lot 5, Section 3, Township 53 North, Range 1 West, Boise Meridian, Bonner
County, Idaho and being described as follows:

Commencing at the Southeast corner of Government Lot 5;

thence North along the East line thereof, 1435 feet, more or less, to a point on
the Southwesterly line of the plat of Lakeview according to the plat thereof,
recorded in Book "B" of Plats, Page 59, records of Bonner County, Idaho;

thence North 69(degrees)07'00" West, 764 feet, more or less, to an aluminum pipe
and cap on the Southeast line of North Gold Creek Lime Placer Survey No. 762;

thence parallel to the West line of Government Lot 5, South 00(degrees)15'29"
West, a distance of 476.10 feet to the Point of Beginning;

thence continuing parallel to the West line of Government Lot 5, South
00(degrees)15'29" West, a distance of 111.91 feet to a found iron rod and PLS
4194 cap;

thence along a line parallel to the South line of Government Lot 5, South
89(degrees)50'40" East, a distance of 111.91 feet;

thence North 44(degrees)47'35" West, a distance of 158.13 feet to the Point of
Beginning.

                                      B-7

<PAGE>

                                                                       EXHIBIT C

                                 (FORM OF BOND)

              THIS BOND IS NON-TRANSFERABLE, EXCEPT TO A SUCCESSOR
                 TRUSTEE UNDER THE INDENTURE REFERRED TO HEREIN.

                               AVISTA CORPORATION

                              First Mortgage Bond,
                             Collateral Series 2004A

REGISTERED                                                            REGISTERED

NO. _________________                                       $___________________

Stated Maturity Date:

            AVISTA CORPORATION, a corporation of the State of Washington
(hereinafter called the Company), for value received, hereby promises to pay to

, as trustee under the Indenture hereinafter referred to or registered assigns,
on the Stated Maturity Date indicated above,

                                                                         DOLLARS

The principal shall be payable upon presentation hereof 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.

            This bond is one of an issue of bonds of the Company issuable in
series and is one of a series known as its First Mortgage Bonds, Collateral
Series 2004A, all bonds of all such issue of series being issued and issuable
under and equally secured (except insofar as any sinking or other fund,
established in accordance with the provisions of the Mortgage hereinafter
mentioned, may afford additional security for the bonds of any particular
series) by a Mortgage and Deed of Trust, dated as of June 1, 1939, executed by
the Company (formerly known as The Washington Water Power Company) to City Bank
Farmers Trust Company and Ralph E. Morton, as Trustees (Citibank, N.A.,
successor Trustee to both said Trustees). Such mortgage and deed of trust has
been amended and supplemented by various supplemental indentures, including the
Thirty-fifth Supplemental Indenture, dated as of December 1, 2004 (the
"Thirty-fifth Supplemental Indenture") and, as so amended and supplemented, is
herein called the

<PAGE>

"Mortgage". Reference is made to the Mortgage for a description of the property
mortgaged and pledged, the nature and extent of the security, the rights of the
holders of the bonds and of the Trustee in respect thereof, the duties and
immunities of the Trustee and the terms and conditions upon which the bonds are
and are to be secured and the circumstances under which additional bonds may be
issued. By its acceptance of this bond, the holder hereof is deemed to have
consented and agreed to all of the terms and provisions of the Mortgage. The
Mortgage may be modified or altered by affirmative vote of the holders of at
least 60% in principal amount of the bonds outstanding under the Mortgage,
considered as one class, or, if the rights of one or more, but less than all,
series of bonds then outstanding are to be affected, then such modification or
alteration may be effected with the affirmative vote only of 60% in principal
amount of the bonds outstanding of the series so to be affected, considered as
one class, and, furthermore, for limited purposes, the Mortgage may be modified
or altered without any consent or other action of holders of any series of
bonds. No modification or alteration shall, however, permit an extension of the
Maturity of the principal of this bond or a reduction in such principal or any
other modification in the terms of payment of such principal or the creation of
any lien equal or prior to the lien of the Mortgage or deprive the holder of a
lien on the mortgaged and pledged property without the consent of the holder
hereof.

            The bonds of this series are redeemable, in whole at any time or in
part from time to time, at the option of the Company at the principal amount
thereof.

            The bonds of this series have been issued and delivered to, and are
to be held by, the Indenture Trustee for the benefit of the Holders of all
Benefitted Securities from time to time outstanding under the Indenture (as such
terms are defined in the Thirty-fifth Supplemental Indenture);

            In the event that the Notes (as defined in the Thirty-fifth
Supplemental Indenture) maturing on June 19, 2028, or any principal amount
thereof, are to be redeemed on June 19, 2008 in accordance with the provisions
thereof, bonds of this series having a Stated Maturity Date of June 19, 2028, in
the principal amount of the Notes so to be redeemed, shall be redeemd on June
19, 2008 at the principal amount thereof.

            In the event that the maturity of all outstanding Benefitted
Securities shall have been accelerated following an Event of Default (as defined
in the Indenture), all outstanding bonds of this series shall be redeemed at the
principal amount thereof (the obligation to effect such redemption being
rescinded upon the rescission of such acceleration);

            The obligation of the Company to pay the principal of bonds of this
series of any stated maturity at or after Maturity shall be deemed to have been
satisfied and discharged to the extent of the amount, if any, paid by the
Company in respect of the corresponding amount of principal then due on the
Notes of the same stated maturity.

            Anything in this bond to the contrary notwithstanding, if, at the
time of the Maturity of the bonds of this series of any stated maturity, the
stated aggregate principal amount of such bonds of such stated maturity then
outstanding shall exceed the aggregate principal

                                      C-2

<PAGE>

amount of Notes of such stated maturity then outstanding under the Indenture,
the aggregate principal amount of such bonds of such stated maturity shall be
deemed to have been reduced by the amount of such excess.

            The principal hereof may be declared or may become due prior to the
stated maturity date on the conditions, in the manner and at the time set forth
in the Mortgage, upon the occurrence of a Completed Default as in the Mortgage
provided.

            This bond is non-transferable except as required to effect transfer
to any successor trustee under the Indenture, any such transfer to be made at
the office or agency of the Company in the Borough of Manhattan, The City of New
York, upon surrender and cancellation of this bond, together with a written
instrument of transfer whenever required by the Company duly executed by the
registered owner or by its duly authorized attorney, and, thereupon, a new fully
registered bond of the same series for a like principal amount will be issued to
the transferee in exchange herefor as provided in the Mortgage. The Company and
the Trustee may deem and treat the person in whose name this bond is registered
as the absolute owner hereof for the purpose of receiving payment and for all
other purposes.

            In the manner prescribed in the Mortgage, any bonds of this series,
upon surrender thereof for cancellation at the office or agency of the Company
in the Borough of Manhattan, The City of New York, are exchangeable for a like
aggregate principal amount of bonds of the same series and stated maturity of
other authorized denominations.

            No recourse shall be had for the payment of the principal of or
interest on this bond against any incorporator or any past, present or future
subscriber to the capital stock, stockholder, officer or director of the Company
or of any predecessor or successor corporation, as such, either directly or
through the Company or any predecessor or successor corporation, under any rule
of law, statute or constitution or by the enforcement of any assessment or
otherwise, all such liability of incorporators, subscribers, stockholders,
officers and directors being released by the holder or owner hereof by the
acceptance of this bond and being likewise waived and released by the terms of
the Mortgage.

            This bond shall not become obligatory until Citibank, N.A., the
Trustee under the Mortgage, or its successor thereunder, shall have signed the
form of certificate endorsed hereon.

                                      C-3

<PAGE>

      IN WITNESS WHEREOF, AVISTA CORPORATION has caused this bond to be signed
in its corporate name by its President or one of its Vice Presidents by his
signature or a facsimile thereof, and its corporate seal to be impressed or
imprinted hereon and attested by its Corporate Secretary or one of its Assistant
Corporate Secretaries by his signature or a facsimile thereof.

Dated:                                  AVISTA CORPORATION

                                        By: ____________________________________

ATTEST: ____________________________

                                      C-4

<PAGE>

                              TRUSTEE'S CERTIFICATE

            This bond is one of the bonds, of the series herein designated,
described or provided for in the within-mentioned Mortgage.

                                        CITIBANK, N.A.
                                        Trustee

                                        By: ____________________________________
                                                    Authorized Officer

                                      C-5

<PAGE>

            FOR VALUE RECEIVED the undersigned hereby sells, assigns and
transfers unto

____________________________________________________
     [please insert social security or other identifying number of assignee]

____________________________________________________
            [please print or typewrite name and address of assignee]

____________________________________________________
the within bond of AVISTA CORPORATION and does hereby irrevocably constitute and
appoint _________________ , Attorney, to transfer said bond on the books of the
within-mentioned Company, will full power of substitution in the premises.

Dated: _________________

       _______________________

                                        Notice: The signature to this assignment
                                        must correspond with the name as written
                                        upon the face of the bond in every
                                        particular without alteration or
                                        enlargement or any change whatsoever.

                                      C-6<PAGE>

                                                                     EXHIBIT 4.3

================================================================================

                               AVISTA CORPORATION

                                       TO

                                 CITIBANK, N.A.

                           As Successor Trustee under
                           Mortgage and Deed of Trust,
                            dated as of June 1, 1939

                            ------------------------

                       THIRTY-SIXTH SUPPLEMENTAL INDENTURE

         Providing among other things for two series of bonds designated
                 "First Mortgage Bonds, Collateral Series 2004B"
                               Due October 1, 2032
                                       and
                 "First Mortgage Bonds, Collateral Series 2004C"
                                Due March 1, 2034

                            ------------------------

                          Dated as of December 1, 2004

================================================================================

<PAGE>

                       THIRTY-SIXTH SUPPLEMENTAL INDENTURE

            THIS INDENTURE, dated as of the 1st day of December 2004, between
AVISTA CORPORATION (formerly known as The Washington Water Power Company), a
corporation of the State of Washington, whose post office address is 1411 East
Mission Avenue, Spokane, Washington 99202 (the "Company"), and CITIBANK, N.A.,
formerly First National City Bank (successor by merger to First National City
Trust Company, formerly City Bank Farmers Trust Company), a national banking
association incorporated and existing under the laws of the United States of
America, whose post office address is 388 Greenwich Street, 14th Floor, New
York, 10013 New York (the "Trustee"), as Trustee under the Mortgage and Deed of
Trust, dated as of June 1, 1939 (the "Original Mortgage"), executed and
delivered by the Company to secure the payment of bonds issued or to be issued
under and in accordance with the provisions thereof, this indenture (the
"Thirty-sixth Supplemental Indenture") being supplemental to the Original
Mortgage, as heretofore supplemented and amended.

            WHEREAS pursuant to a written request of the Company made in
accordance with Section 103 of the Original Mortgage, Francis M. Pitt (then
Individual Trustee under the Mortgage, as supplemented) ceased to be a trustee
thereunder on July 23, 1969, and all of his powers as Individual Trustee have
devolved upon the Trustee and its successors alone; and

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

            WHEREAS the Company has heretofore executed and delivered, in
addition to the Original Mortgage, the indentures supplemental thereto, and has
issued the series of bonds, set forth in Exhibit A hereto (the Original
Mortgage, as supplemented and amended by the First through Thirty-fifth
Supplemental Indentures, being herein sometimes called the "Mortgage"); and

            WHEREAS the Original Mortgage and the First through Thirty-third
Supplemental Indentures have been appropriately filed or recorded in various
official records in the States of Washington, California, Idaho, Montana and
Oregon, as set forth in the First through Thirty-fourth supplemental Indentures
and the Instrument of Further Assurance, dated December 15, 2001, hereinafter
referred to; and

            WHEREAS the Thirty-fourth Supplemental Indenture, dated as of
November 1, 2004, and the Thirty-fifth Supplemental Indenture, dated as of
December 1, 2004, are to be appropriately filed or recorded; and

            WHEREAS for the purpose of confirming or perfecting the lien of the
Mortgage on certain of its properties, the Company has heretofore executed and
delivered a Short Form Mortgage and Security Agreement, in multiple counterparts
dated as of various dates in 1992, and such instrument has been appropriately
filed or recorded in the various official records in the States of California,
Montana and Oregon; and

<PAGE>

            WHEREAS for the purpose of confirming or perfecting the lien of the
Mortgage on certain of its properties, the Company has heretofore executed and
delivered an Instrument of Further Assurance, dated as of December 15, 2001, and
such instrument has been appropriately filed or recorded in the various official
records in the States of Washington, California, Idaho, Montana and Oregon; and

            WHEREAS in addition to the property described in the Mortgage the
Company has acquired certain other property, rights and interests in property;
and

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

            WHEREAS the Company now desires to create two new series of bonds;
and

            WHEREAS the execution and delivery by the Company of this
Thirty-sixth Supplemental Indenture, and the terms of the bonds of the
Thirty-fourth and Thirty-fifth Series, hereinafter referred to, have been duly
authorized by the Board of Directors of the Company by appropriate Resolutions
of said Board of Directors, and all things necessary to make this Thirty-sixth
Supplemental Indenture a valid, binding and legal instrument have been
performed;

            NOW, THEREFORE, THIS INDENTURE WITNESSETH: That the Company, in
consideration of the premises and of other good and valuable consideration, the
receipt and sufficiency whereof are hereby acknowledged, hereby confirms the
estate, title and rights of the Trustee (including, without limitation, the lien
of the Mortgage on the property of the Company subjected thereto, whether now
owned or hereafter acquired) held as security for the payment of both the
principal of and interest and premium, if any, on the bonds from time to time
issued under the Mortgage according to their tenor and effect and the
performance of all the provisions of the Mortgage and of such bonds, and,
without limiting the generality of the foregoing, hereby

                                       2
<PAGE>

confirms the grant, bargain, sale, release, conveyance, assignment, transfer,
mortgage, pledge, setting over and confirmation unto the Trustee, contained in
the Mortgage, of all the following described properties of the Company, whether
now owned or hereafter acquired, namely:

            All of the property, real, personal and mixed, of every character
      and wheresoever situated (except any hereinafter or in the Mortgage
      expressly excepted) which the Company now owns or, subject to the
      provisions of Section 87 of the Original Mortgage, may hereafter acquire
      prior to the satisfaction and discharge of the Mortgage, as fully and
      completely as if herein or in the Mortgage specifically described, and
      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 Mortgage) all lands, real estate, easements,
      servitudes, rights of way and leasehold and other interests in real
      estate; all rights to the use or appropriation of water, flowage rights,
      water storage rights, flooding rights, and other rights in respect of or
      relating to water; all plants for the generation of electricity, power
      houses, dams, dam sites, reservoirs, flumes, raceways, diversion works,
      head works, waterways, water works, water systems, gas plants, steam heat
      plants, hot water plants, ice or refrigeration plants, stations,
      substations, offices, buildings and other works and structures and the
      equipment thereof and all improvements, extensions and additions thereto;
      all generators, machinery, engines, turbines, boilers, dynamos,
      transformers, motors, electric machines, switchboards, regulators, meters,
      electrical and mechanical appliances, conduits, cables, pipes and mains;
      all lines and systems for the transmission and distribution of electric
      current, gas, steam heat or water for any purpose; all towers, mains,
      pipes, poles, pole lines, conduits, cables, wires, switch racks,
      insulators, compressors, pumps, fittings, valves and connections; all
      motor vehicles and automobiles; all tools, implements, apparatus,
      furniture, stores, supplies and equipment; all franchises (except the
      Company's franchise to be a corporation), licenses, permits, rights,
      powers and privileges; and (except as hereinafter or in the Mortgage
      expressly excepted) all the right, title and interest of the Company in
      and to all other property of any kind or nature.

            TOGETHER WITH all and singular the tenements, hereditaments 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 Original 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.

            THE COMPANY HEREBY CONFIRMS that, subject to the provisions of
Section 87 of the Original Mortgage, all the property, rights, and franchises
acquired by the Company after the date thereof (except any hereinbefore or
hereinafter or in the Mortgage expressly excepted) are and shall be as fully
embraced within the lien of the Mortgage as if such property, rights and
franchises had been owned by the Company at the date of the Original Mortgage
and had been specifically described therein.

                                       3
<PAGE>

            PROVIDED THAT the following were not and were not intended to be
then or now or hereafter granted, bargained, sold, released, conveyed, assigned,
transferred, mortgaged, pledged, set over or confirmed under the Mortgage and
were, are and shall be expressly excepted from the lien and operation namely:
(l) cash, shares of stock and obligations (including bonds, notes and other
securities) not hereafter specifically pledged, paid, deposited or delivered
under the Mortgage or covenanted so to be; (2) merchandise, equipment, materials
or supplies held for the purpose of sale in the usual course of business or for
consumption in the operation of any properties of the Company; (3) bills, notes
and accounts receivable, and all contracts, leases and operating agreements not
specifically pledged under the Mortgage or covenanted so to be; (4) electric
energy 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 (5) any property heretofore released pursuant to any
provisions of the Mortgage and not heretofore disposed of by the Company;
provided, however, that the property and rights expressly excepted 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 that the
Trustee or a receiver or trustee shall enter upon and take possession of the
Mortgaged and Pledged Property in the manner provided in Article XII of the
Original Mortgage by reason of the occurrence of a Completed Default as defined
in said Article XII.

            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 in the Mortgage as aforesaid, or
intended so to be, unto the Trustee, and its successors, heirs 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 set forth in the Mortgage, this Thirty-sixth Supplemental Indenture
being supplemental to the Mortgage.

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

            The Company further covenants and agrees to and with the Trustee and
its successor or successors in such trust under the Mortgage, as follows:

                                       4
<PAGE>

                                   ARTICLE I

                          THIRTY-FOURTH SERIES OF BONDS

            SECTION 1. (I) There shall be a series of bonds designated
"Collateral Series 2004B" (herein sometimes referred to as the "Thirty-fourth
Series"), each of which shall also bear the descriptive title First Mortgage
Bond, and the form thereof, which has been established by Resolution of the
Board of Directors of the Company, is set forth on Exhibit B hereto. Bonds of
the Thirty-fourth Series shall be issued as fully registered bonds in
denominations of One Thousand Dollars and, at the option of the Company, any
amount in excess thereof (the exercise of such option to be evidenced by the
execution and delivery thereof) and shall be dated as in Section 10 of the
Mortgage provided. Each bond of the Thirty-fourth Series shall mature on October
1, 2032 and shall bear interest, be redeemable and have such other terms and
provisions as set forth below.

            (II)  The Bonds of the Thirty-fourth Series shall have the following
terms and characteristics:

            (a)   the Bonds of the Thirty-fourth Series shall be initially
      authenticated and delivered under the Mortgage in the aggregate principal
      amount of $66,700,000, which principal amount is equal to the outstanding
      aggregate principal amount of the 1999A Revenue Bonds;

            (b)   the Bonds of the Thirty-fourth Series shall bear interest at
      the same rate or rates as shall be in effect from time to time in respect
      of the 1999A Revenue Bonds; and interest on such bonds shall be payable at
      the same times as interest is payable on the 1999A Revenue Bonds;

            (c)   the principal of and interest on each bond of the
      Thirty-fourth Series payable at Maturity shall be payable upon
      presentation thereof at the office or agency of the Company in the Borough
      of Manhattan, The City of New York, in such coin or currency as at the
      time of payment is legal tender for public and private debts. The interest
      on each Bond of the Thirty-fourth Series (other than interest payable at
      Maturity) shall be payable directly to the registered owner thereof;

            (d)   the Bonds of the Thirty-fourth Series shall not be
      redeemable, in whole or in part, at the option of the Company;

            (e)   (i) the Bonds of the Thirty-fourth Series are to be issued and
      delivered to Ambac pursuant to the Bond Delivery Agreement relating to
      such Bonds;

                  (ii)  in the event that any 1999A Revenue Bonds are to be
      redeemed pursuant to Section 4.03 of the 1999A Revenue Bond Indenture
      following a Determination of Taxability (as defined in the 1999A Revenue
      Bond Indenture), Bonds of the Thirty-fourth Series, in a principal amount
      equal to the principal amount of 1999A Revenue Bonds to be redeemed, shall
      be redeemed on the date fixed for redemption of

                                       5
<PAGE>

      the 1999A Revenue Bonds, at the principal amount thereof plus accrued
      interest to the redemption date;

                  (iii) in the event that all 1999A Revenue Bonds have become
      immediately due and payable pursuant to Section 9.02(a) of the 1999A
      Revenue Bond Indenture following the occurrence of an Event of Default (as
      defined in the 1999A Revenue Bond Indenture), the Bonds of the
      Thirty-fourth Series shall thereupon be redeemed at the principal amount
      thereof plus accrued interest to the redemption date (the obligation to
      effect such redemption being rescinded upon the rescission of such
      acceleration);

                  (iv)  the obligation of the Company to make any payment of the
      principal of or interest on the Bonds of the Thirty-fourth Series shall be
      deemed to have been satisfied and discharged to the extent of the sum of

                  (A)   the amount, if any, credited under the 1999A Loan
            Agreement against the obligation of the Company to make payment in
            respect of the corresponding amount of principal of or interest on
            the 1999A Revenue Bonds;

                  (B)   the amount, if any, paid by the Company pursuant to the
            1999A Loan Agreement in respect of such corresponding amount of
            principal of or interest on the 1999A Revenue Bonds; and

                  (C)   if Ambac shall have made a payment in respect of such
            corresponding amount of principal of or interest on the 1999A
            Revenue Bonds pursuant to the Policy, the amount, if any, paid by
            the Company pursuant to the Insurance Agreement to reimburse Ambac
            for such payment;

                  (v)   the Trustee shall be entitled to presume that the
      obligation of the Company to pay the principal of and interest on the
      Bonds of the Thirty-fourth 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 Ambac, signed by an authorized officer
      thereof, stating that the principal of and/or interest on the Bonds of the
      Thirty-fourth Series has become due and payable and has not been fully
      paid, and specifying the amount of funds required to make such payment;

            (f)   no service charge shall be made for the registration of
      transfer or exchange of Bonds of the Thirty-fourth Series;

            (g)   in the event of an application by Ambac for a substituted Bond
      of the Thirty-fourth Series pursuant to Section 16 of the Original
      Mortgage, Ambac shall not be required to provide any indemnity or pay any
      expenses or charges as contemplated in said Section 16; and

            (h)   the Bonds of the Thirty-fourth Series shall have such other
      terms as are set forth in the form of bond attached hereto as Exhibit B.

                                       6
<PAGE>

            Anything in this Supplemental Indenture or in the Bonds of the
Thirty-fourth Series to the contrary notwithstanding, if, at the time of the
Maturity of the Bonds of the Thirty-fourth Series, the stated aggregate
principal amount of such Bonds then Outstanding shall exceed the aggregate
principal amount of 1999A Revenue Bonds then outstanding, the aggregate
principal amount of such Bonds shall be deemed to have been reduced by the
amount of such excess.

            (III) For all purposes of this Article I, except as otherwise
expressly provided or unless the context otherwise requires, the terms defined
below shall have the meanings specified:

            "AMBAC" means Ambac Assurance Corporation, a Wisconsin-domiciled
      stock insurance company or any successor thereto as obligor on the Policy.

            "BOND DELIVERY AGREEMENT" means, with respect the Bonds of the
      Thirty-fourth Series, the Bond Delivery Agreement, dated December 15,
      2004, between the Company and Ambac, relating to such Bonds.

            "CITY" means the City of Forsyth, Montana, a political subdivision
      of the State of Montana.

            "INSURANCE AGREEMENT" means the Insurance Agreement, dated as of
      September 1, 1999, between Ambac and the Company, as supplemented by the
      Insurance Agreement, dated as of January 1, 2002, between Ambac and the
      Company.

            "POLICY" means the municipal bond insurance policy issued by Ambac
      with respect to the 1999A Revenue Bonds.

            "1999A LOAN AGREEMENT" means the Loan Agreement, dated as of
      September 1, 1999, between the City and the Company, relating to the 1999A
      Revenue Bonds.

            "1999A REVENUE BONDS" means the Pollution Control Revenue Refunding
      Bonds (Avista Corporation Colstrip Project) Series 1999A issued by the
      City.

            "1999A REVENUE BOND INDENTURE" means the Trust Indenture, dated as
      of September 1, 1999, between the City and JPMorgan Chase Bank (successor
      by merger to Chase Manhattan Bank and Trust Company, National
      Association), trustee, relating to the 1999A Revenue Bonds.

            "1999A REVENUE BOND TRUSTEE" means the trustee under the 1999A
      Revenue Bond Indenture.

            Copies of the 1999A Revenue Bond Indenture, the 1999A Loan Agreement
and the Policy are on file at the office of the 1999A Revenue Bond Trustee at
560 Mission Street, 13th Floor, San Francisco, CA 94105 and at the office of the
Company at 1411 East Mission Avenue, Spokane, WA 99202.

                                        7
<PAGE>

                                   ARTICLE II

                          THIRTY-FIFTH SERIES OF BONDS

            SECTION 1. (I) There shall be a series of bonds designated
"Collateral Series 2004C" (herein sometimes referred to as the "Thirty-fifth
Series"), each of which shall also bear the descriptive title First Mortgage
Bond, and the form thereof, which has been established by Resolution of the
Board of Directors of the Company, is set forth on Exhibit B hereto. Bonds of
the Thirty-fifth Series shall be issued as fully registered bonds in
denominations of One Thousand Dollars and, at the option of the Company, any
amount in excess thereof (the exercise of such option to be evidenced by the
execution and delivery thereof) and shall be dated as in Section 10 of the
Mortgage provided. Each bond of the Thirty-fifth Series shall mature on March 1,
2034 and shall bear interest, be redeemable and have such other terms and
provisions as set forth below.

            (II)  The Bonds of the Thirty-fifth Series shall have the following
terms and characteristics:

            (a)   the Bonds of the Thirty-fifth Series shall be initially
      authenticated and delivered under the Mortgage in the aggregate principal
      amount of $17,000,000, which principal amount is equal to the outstanding
      aggregate principal amount of the 1999B Revenue Bonds;

            (b)   the Bonds of the Thirty-fifth Series shall bear interest at
      the same rate or rates as shall be in effect from time to time in respect
      of the 1999B Revenue Bonds; and interest on such bonds shall be payable at
      the same times as interest is payable on the 1999B Revenue Bonds;

            (c)   the principal of and interest on each bond of the Thirty-fifth
      Series payable at Maturity shall be payable upon presentation thereof at
      the office or agency of the Company in the Borough of Manhattan, The City
      of New York, in such coin or currency as at the time of payment is legal
      tender for public and private debts. The interest on each Bond of the
      Thirty-fifth Series (other than interest payable at Maturity) shall be
      payable directly to the registered owner thereof;

            (d)   the Bonds of the Thirty-fifth Series shall not be redeemable,
      in whole or in part, at the option of the Company;

            (e)   (i) the Bonds of the Thirty-fifth Series are to be issued and
      delivered to Ambac pursuant to the Bond Delivery Agreement relating to
      such Bonds;

                  (ii)  in the event that any 1999B Revenue Bonds are to be
      redeemed pursuant to Section 4.03 of the 1999B Revenue Bond Indenture
      following a Determination of Taxability (as defined in the 1999B Revenue
      Bond Indenture), Bonds of the Thirty-fifth Series, in a principal amount
      equal to the principal amount of 1999B Revenue Bonds to be redeemed, shall
      be redeemed on the date fixed for redemption of

                                       8
<PAGE>

      the 1999B Revenue Bonds, at the principal amount thereof plus accrued
      interest to the redemption date;

                  (iii) in the event that all 1999B Revenue Bonds have become
      immediately due and payable pursuant to Section 9.02(a) of the 1999B
      Revenue Bond Indenture following the occurrence of an Event of Default (as
      defined in the 1999B Revenue Bond Indenture), the Bonds of the
      Thirty-fifth Series shall thereupon be redeemed at the principal amount
      thereof plus accrued interest to the redemption date (the obligation to
      effect such redemption being rescinded upon the rescission of such
      acceleration);

                  (iv)  the obligation of the Company to make any payment of the
      principal of or interest on the Bonds of the Thirty-fifth Series shall be
      deemed to have been satisfied and discharged to the extent of the sum of

                  (A)   the amount, if any, credited under the 1999B Loan
            Agreement against the obligation of the Company to make payment in
            respect of the corresponding amount of principal of or interest on
            the 1999B Revenue Bonds;

                  (B)   the amount, if any, paid by the Company pursuant to the
            1999B Loan Agreement in respect of such corresponding amount of
            principal of or interest on the 1999B Revenue Bonds; and

                  (C)   if Ambac shall have made a payment in respect of such
            corresponding amount of principal of or interest on the 1999B
            Revenue Bonds pursuant to the Policy, the amount, if any, paid by
            the Company pursuant to the Insurance Agreement to reimburse Ambac
            for such payment;

                  (v)   the Trustee shall be entitled to presume that the
      obligation of the Company to pay the principal of and interest on the
      Bonds of the Thirty-fifth 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 Ambac, signed by an authorized officer
      thereof, stating that the principal of and/or interest on the Bonds of the
      Thirty-fifth Series has become due and payable and has not been fully
      paid, and specifying the amount of funds required to make such payment;

            (f)   no service charge shall be made for the registration of
      transfer or exchange of Bonds of the Thirty-fifth Series;

            (g)   in the event of an application by Ambac for a substituted Bond
      of the Thirty-fifth Series pursuant to Section 16 of the Original
      Mortgage, Ambac shall not be required to provide any indemnity or pay any
      expenses or charges as contemplated in said Section 16; and

            (h)   the Bonds of the Thirty-fifth Series shall have such other
      terms as are set forth in the form of bond attached hereto as Exhibit B.

                                        9
<PAGE>

            Anything in this Supplemental Indenture or in the Bonds of the
Thirty-fifth Series to the contrary notwithstanding, if, at the time of the
Maturity of the Bonds of the Thirty-fifth Series, the stated aggregate principal
amount of such Bonds then Outstanding shall exceed the aggregate principal
amount of 1999B Revenue Bonds then outstanding, the aggregate principal amount
of such Bonds shall be deemed to have been reduced by the amount of such excess.

            (III) For all purposes of this Article II, except as otherwise
expressly provided or unless the context otherwise requires, the terms defined
below shall have the meanings specified:

            "AMBAC" means Ambac Assurance Corporation, a Wisconsin-domiciled
      stock insurance company or any successor thereto as obligor on the Policy.

            "BOND DELIVERY AGREEMENT" means, with respect to the Bonds of the
      Thirty-fifth Series, the Bond Delivery Agreement, dated December 15, 2004,
      between the Company and Ambac, relating to such Bonds.

            "CITY" means the City of Forsyth, Montana, a political subdivision
      of the State of Montana.

            "INSURANCE AGREEMENT" means the Insurance Agreement, dated as of
      September 1, 1999, between Ambac and the Company, as supplemented by the
      Insurance Agreement, dated as of January 1, 2002, between Ambac and the
      Company.

            "POLICY" means the municipal bond insurance policy issued by Ambac
      with respect to the 1999B Revenue Bonds.

            "1999B LOAN AGREEMENT" means the Loan Agreement, dated as of
      September 1, 1999, between the City and the Company, relating to the 1999B
      Revenue Bonds.

            "1999B REVENUE BONDS" means the Pollution Control Revenue Refunding
      Bonds (Avista Corporation Colstrip Project) Series 1999B issued by the
      City.

            "1999B REVENUE BOND INDENTURE" means the Trust Indenture, dated as
      of September 1, 1999, between the City and JPMorgan Chase Bank, N.A.
      (successor by merger to Chase Manhattan Bank and Trust Company, National
      Association), trustee, relating to the 1999B Revenue Bonds.

            "1999B REVENUE BOND TRUSTEE" means the trustee under the 1999B
      Revenue Bond Indenture.

            Copies of the 1999B Revenue Bond Indenture, the 1999B Loan Agreement
and the Policy are on file at the office of the 1999B Revenue Bond Trustee at
560 Mission Street, 13th Floor, San Francisco, CA 94105 and at the office of the
Company at 1411 East Mission Avenue, Spokane, WA 99202.

                                       10
<PAGE>

                                   ARTICLE III
                                OUTSTANDING BONDS

            Upon the delivery of this Thirty-sixth Supplemental Indenture, Bonds
of the Thirty-fourth Series in the aggregate principal amount of $66,700,000 and
Bonds of the Thirty-fifth Series in the aggregate principal amount of
$17,000,000 are to be issued and will be Outstanding, in addition to
$872,350,000 aggregate principal amount of bonds of prior series Outstanding at
the date of delivery of this Thirty-sixth Supplemental Indenture.

                                   ARTICLE IV

                              PROSPECTIVE AMENDMENT

            SECTION 1. The owners of the Bonds of the Thirty-fourth and
Thirty-fifth Series shall be deemed to have consented to the amendment of
Section 28 of the Original Mortgage to add at the end thereof a new paragraph
reading as follows:

            Notwithstanding the foregoing, any Opinion of Counsel delivered
      pursuant to subdivision (7) of this Section 28, or pursuant to any other
      provision of this Indenture by reference to this Section 28, may, at the
      election of the Company, omit any or all of the statements contained in
      clause (a) of subdivision (7) if there shall have been delivered to the
      Trustee a policy of title insurance (or endorsement thereto) issued by a
      nationally recognized title insurance company, in an amount not less than
      twenty-eight percent (28%)(1) of the cost or fair value to the Company
      (whichever is less) of the Property Additions made the basis of such
      application, insuring, in customary terms, against risk of loss sustained
      or incurred by the Trustee by reason of any circumstances or conditions by
      virtue of which the statements omitted from clause (a) of such Opinion of
      Counsel would not have been accurate if made.

                                    ARTICLE V

                            MISCELLANEOUS PROVISIONS

            SECTION 1. The terms defined in the Original Mortgage shall, for all
purposes of this Thirty-sixth Supplemental Indenture, have the meanings
specified in the Original Mortgage.

            SECTION 2. The Trustee hereby confirms its acceptance of the trusts
in the Original Mortgage declared, provided, created or supplemented and agrees
to perform the same upon the terms and conditions in the Original Mortgage set
forth, including the following:

------------

      (1) The owners of the Bonds of the Thirty-fourth and Thirty-fifth Series
shall be deemed to have consented to the amendment contained in this Section 1
of Article II, either with the percentage shown above or with any higher
percentage.

                                       11
<PAGE>

            The Trustee shall not be responsible in any manner whatsoever for or
in respect of the validity or sufficiency of this Thirty-sixth Supplemental
Indenture or for or in respect of the recitals contained herein, all of which
recitals are made by the Company solely. Each and every term and condition
contained in Article XVI of the Original Mortgage, shall apply to and form part
of this Thirty-sixth 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 Thirty-sixth Supplemental Indenture.

            SECTION 3. Whenever in this Thirty-sixth Supplemental Indenture
either of the parties hereto is named or referred to, this shall, subject to the
provisions of Articles XV and XVI of the Original Mortgage be deemed to include
the successors and assigns of such party, and all the covenants and agreements
in this Thirty-sixth Supplemental Indenture contained by or on behalf of the
Company, or by or on behalf of the Trustee, or either of them, shall, subject as
aforesaid, bind and inure to the respective benefits of the respective
successors and assigns of such parties, whether so expressed or not.

            SECTION 4. Nothing in this Thirty-sixth Supplemental Indenture,
expressed or implied, is intended, or shall be construed, to confer upon, or to
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 Thirty-sixth Supplemental Indenture
or any covenant, condition, stipulation, promise or agreement hereof, and all
the covenants, conditions, stipulations, promises and agreements in this
Thirty-sixth Supplemental Indenture contained by or 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 5. This Thirty-sixth 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 6. The titles of the several Articles of this Thirty-sixth
Supplemental Indenture shall not be deemed to be any part thereof.

                            ------------------------

                                       12
<PAGE>

            IN WITNESS WHEREOF, on the __th day of December __, 2004, AVISTA
CORPORATION 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 Corporate Secretary or
one of its Assistant Corporate Secretaries for and in its behalf, all in The
City of Spokane, Washington, as of the day and year first above written; and on
the ___th day of December, 2004, CITIBANK, N.A., 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 or one of its Senior Trust Officers or
one of its Trust Officers and its corporate seal to be attested by one of its
Vice Presidents or one of its Trust Officers, all in The City of New York, New
York, as of the day and year first above written.

                                           AVISTA CORPORATION

                                           By:  /s/ Malyn K. Malquist
                                               ---------------------------------
                                                    Senior Vice President

Attest:

       /s/ Susan Y. Miner
---------------------------------
  Assistant Corporate Secretary

Executed, sealed and delivered
  by AVISTA CORPORATION
  in the presence of:

       /s/ Diane C. Thoren
---------------------------------
       Diane C. Thoren

       /s/ Paul W. Kimball
---------------------------------
       Paul W. Kimball

                                       13
<PAGE>

                                           CITIBANK, N.A., AS TRUSTEE

                                            By:  /s/ Wafaa Orfy
                                               ---------------------------------
                                                  Wafaa Orfy, Vice President

Attest:

          /s/ Nancy Forte
-------------------------------------
Nancy Forte, Assistant Vice President

Executed, sealed and delivered
   by CITIBANK, N.A.,
   as trustee. in the presence of:

          /s/ R.T. Kirchner
-------------------------------------
           R. T. Kirchner, Vice President

          /s/ John J. Byrnes
-------------------------------------
           John J. Byrnes, Vice President

                                       14
<PAGE>

STATE OF WASHINGTON    )
                       ) ss.:
COUNTY OF SPOKANE      )

            On the 15th day of December 2004, before me personally appeared
Malyn Malquist, to me known to be a Senior Vice President of AVISTA CORPORATION,
one of the corporations that executed the within and foregoing instrument, and
acknowledged said instrument to be the free and voluntary act and deed of said
Corporation for the uses and purposes therein mentioned and on oath stated that
he was authorized to execute said instrument and that the seal affixed is the
corporate seal of said Corporation.

            On the 15th day of December 2004, before me, Sue Miner, a Notary
Public in and for the State and County aforesaid, personally appeared Malyn
Malquist, known to me to be a Senior Vice President of AVISTA CORPORATION, one
of the corporations that executed the within and foregoing instrument and
acknowledged to me that such Corporation executed the same.

            IN WITNESS WHEREOF, I have hereunto set my hand and affixed my
official seal the day and year first above written.

                                            /s/ Susan Y. Miner
                                           -------------------------------------
                                                            Notary Public

                                            Sue Miner
                                            Notary Public
                                            Commission Expires August 20, 2007
                                            State of Washington

                                       15
<PAGE>

STATE OF NEW YORK     )
                      ) ss.:
COUNTY OF NEW YORK    )

            On the 13th day of December 2004, before me personally appeared
Wafaa Orfy, to me known to be a Vice President of CITIBANK, N.A., one of the
corporations that executed the within and foregoing instrument, and acknowledged
said instrument to be the free and voluntary act and deed of said Corporation
for the uses and purposes therein mentioned and on oath stated that he was
authorized to execute said instrument and that the seal affixed is the corporate
seal of said Corporation.

            On the 13th day of December 2004, before me, a Notary Public in and
for the State and County aforesaid, personally appeared Wafaa Orfy, known to me
to be an Vice President of CITIBANK, N.A., one of the corporations that executed
the within and foregoing instrument and acknowledged to me that such Corporation
executed the same.

            IN WITNESS WHEREOF, I have hereunto set my hand and affixed my
official seal the day and year first above written.

                                   /s/ Nanette Murphy
                                 -----------------------------------------------
                                                    Notary Public

                                                NANETTE MURPHY
                                                Notary Public, State of New York
                                                No. 01MU6086415
                                                Qualified in Kings County
                                                Commission Expires 1/21/07

                                       16
<PAGE>

                                                                       EXHIBIT A

                        MORTGAGE, SUPPLEMENTAL INDENTURES
                               AND SERIES OF BONDS

<TABLE>
<CAPTION>
 MORTGAGE OR                                  SERIES                                PRINCIPAL
 SUPPLEMENTAL                      -------------------------------    PRINCIPAL      AMOUNT
  INDENTURE        DATED AS OF     NO.         DESIGNATION          AMOUNT ISSUED  OUTSTANDING
--------------  -----------------  ---  --------------------------  -------------  -----------
<S>             <C>                <C>  <C>                         <C>            <C>
Original        June 1, 1939       1      3-1/2% Series due 1964    $ 22,000,000      None
First           October 1, 1952    2      3-3/4% Series due 1982      30,000,000      None
Second          May 1, 1953        3      3-7/8% Series due 1983      10,000,000      None
Third           December 1, 1955                   None
Fourth          March 15, 1957                     None
Fifth           July 1, 1957       4      4-7/8% Series due 1987      30,000,000      None
Sixth           January 1, 1958    5      4-1/8% Series due 1988      20,000,000      None
Seventh         August 1, 1958     6      4-3/8% Series due 1988      15,000,000      None
Eighth          January 1, 1959    7      4-3/4% Series due 1989      15,000,000      None
Ninth           January 1, 1960    8      5-3/8% Series due 1990      10,000,000      None
Tenth           April 1, 1964      9      4-5/8% Series due 1994      30,000,000      None
Eleventh        March 1, 1965      10     4-5/8% Series due 1995      10,000,000      None
Twelfth         May 1, 1966                        None
Thirteenth      August 1, 1966     11       6% Series due 1996        20,000,000      None
Fourteenth      April 1, 1970      12     9-1/4% Series due 2000      20,000,000      None
Fifteenth       May 1, 1973        13     7-7/8% Series due 2003      20,000,000      None
Sixteenth       February 1, 1975   14     9-3/8% Series due 2005      25,000,000      None
Seventeenth     November 1, 1976   15     8-3/4% Series due 2006      30,000,000      None
Eighteenth      June 1, 1980                       None
Nineteenth      January 1, 1981    16    14-1/8% Series due 1991      40,000,000      None
Twentieth       August 1, 1982     17       15-3/4% Series due        60,000,000      None
1990-1992
Twenty-First    September 1, 1983  18    13-1/2% Series due 2013      60,000,000      None
Twenty-Second   March 1, 1984      19    13-1/4% Series due 1994      60,000,000      None
Twenty-Third    December 1, 1986   20     9-1/4% Series due 2016      80,000,000      None
Twenty-Fourth   January 1, 1988    21    10-3/8% Series due 2018      50,000,000      None
Twenty-Fifth    October 1, 1989    22     7-1/8% Series due 2013      66,700,000      None
                                   23     7-2/5% Series due 2016      17,000,000      None
Twenty-Sixth    April 1, 1993      24      Secured Medium-Term       250,000,000    89,500,000
                                             Notes, Series A
                                        ($250,000,000 authorized)
Twenty-Seventh  January 1, 1994    25      Secured Medium-Term       161,000,000    59,000,000
                                             Notes, Series B
                                        ($250,000,000 authorized)
Twenty-Eighth   September 1, 2001  26   Collateral Series due 2002   220,000,000      None
Twenty-Ninth    December 1, 2001   27     7.75% Series due 2007      150,000,000   150,000,000
Thirtieth       May 1, 2002        28   Collateral Series due 2003   225,000,000      None
Thirty-First    May 1, 2003        29   Collateral Series due 2004   245,000,000      None
Thirty-Second   September 1, 2003  30     6.125% Series due 2013      45,000,000    45,000,000
Thirty-Third    May 1, 2004        31   Collateral Series due 2005   350,000,000   350,000,000
Thirty-Fourth   November 1, 2004   32     5.45% Series due 2019       90,000,000    90,000,000
Thirty-Fifth    December 1, 2004   33    Collateral Series 2004A      88,850,000    88,850,000
</TABLE>

                                       B-1
<PAGE>

                                                                       EXHIBIT B

                                 (FORM OF BOND)

              THIS BOND IS NON-TRANSFERABLE, EXCEPT TO A SUCCESSOR
                    OBLIGOR ON THE POLICY REFERRED TO HEREIN.

                               AVISTA CORPORATION

                              First Mortgage Bond,
                             Collateral Series 2004_

REGISTERED                                                            REGISTERED

NO. _____________                                                 $_____________

            AVISTA CORPORATION, a corporation of the State of Washington
(hereinafter called the Company), for value received, hereby promises to pay to

                           Ambac Assurance Corporation

or registered assigned on____________________

                                                                         DOLLARS

and to pay the registered owner hereof interest thereon at the respective rate
or rates as shall be in effect from time to time in respect of the 1999_ Revenue
Bonds (as defined in the Supplemental Indenture hereinafter referred to) until
the Company's obligation with respect to the payment of such principal shall
have been discharged; and such interest shall be payable at the same times as
interest is payable on the 1999_ Revenue Bonds. The principal of and premium, if
any, and interest on this bond payable at Maturity (as hereinafter defined)
shall be payable upon presentation hereof 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. The interest on this bond (other than interest payable
at Maturity) shall be paid directly to the registered owner hereof. Interest
payable at Maturity shall be paid to the person to whom principal shall be paid.
As used herein, the term "Maturity" shall mean the date on which the principal
of this bond becomes due and payable, whether at stated maturity, upon
redemption or acceleration, or otherwise.

            This bond is one of an issue of bonds of the Company issuable in
series and is one of a series known as its First Mortgage Bonds, Collateral
Series 2004_, all bonds of all such issue of series being issued and issuable
under and equally secured (except insofar as any sinking or other fund,
established in accordance with the provisions of the Mortgage hereinafter
mentioned, may afford additional security for the bonds of any particular
series) by a Mortgage and Deed of Trust, dated as of June 1, 1939, executed by
the Company (formerly known as The Washington Water Power Company) to City Bank
Farmers Trust Company and Ralph E.

                                       B-1
<PAGE>

Morton, as Trustees (Citibank, N.A., successor Trustee to both said Trustees).
Such mortgage and deed of trust has been amended and supplemented by various
supplemental indentures, including the Thirty-sixth Supplemental Indenture,
dated as of December 1, 2004 (the "Thirty-sixth Supplemental Indenture") and, as
so amended and supplemented, is herein called the "Mortgage". Reference is made
to the Mortgage for a description of the property mortgaged and pledged, the
nature and extent of the security, the rights of the holders of the bonds and of
the Trustee in respect thereof, the duties and immunities of the Trustee and the
terms and conditions upon which the bonds are and are to be secured and the
circumstances under which additional bonds may be issued. By its acceptance of
this bond, the holder hereof is deemed to have consented and agreed to all of
the terms and provisions of the Mortgage. The Mortgage may be modified or
altered by affirmative vote of the holders of at least 60% in principal amount
of the bonds outstanding under the Mortgage, considered as one class, or, if the
rights of one or more, but less than all, series of bonds then outstanding are
to be affected, then such modification or alteration may be effected with the
affirmative vote only of 60% in principal amount of the bonds outstanding of the
series so to be affected, considered as one class, and, furthermore, for limited
purposes, the Mortgage may be modified or altered without any consent or other
action of holders of any series of bonds. No modification or alteration shall,
however, permit an extension of the Maturity of the principal of, or interest
on, this bond or a reduction in such principal or the rate of interest hereon or
any other modification in the terms of payment of such principal or interest or
the creation of any lien equal or prior to the lien of the Mortgage or deprive
the holder of a lien on the mortgaged and pledged property without the consent
of the holder hereof.

            The bonds of this series are not redeemable, in whole or in part, at
the option of the Company.

            The bonds of this series have been issued and delivered to Ambac
pursuant to the Insurance Agreement (as such terms are defined in the
Thirty-sixth Supplemental Indenture).

            In the event that any 1999_ Revenue Bonds are to be redeemed
pursuant to Section 4.03 of the 1999_ Revenue Bond Indenture (as defined in the
Thirty-sixth Supplemental Indenture) following a Determination of Taxability (as
defined in the 1999_ Revenue Bond Indenture), bonds of this series, in a
principal amount equal to the principal amount of 1999_ Revenue Bonds to be
redeemed, shall be redeemed on the date fixed for redemption of the 1999_
Revenue Bonds, at the principal amount thereof plus accrued interest to the
redemption date.

            In the event that all 1999_ Revenue Bonds have become immediately
due and payable pursuant to Section 9.02(a) of the 1999_ Revenue Bond Indenture
following the occurrence of an Event of Default (as defined in the 1999_ Revenue
Bond Indenture), the bonds of the this series shall thereupon be redeemed at the
principal amount thereof plus accrued interest to the redemption date (the
obligation to effect such redemption being rescinded upon the rescission of such
acceleration);

            The obligation of the Company to make any payment of the principal
of or interest on the bonds of this series shall be deemed to have been
satisfied and discharged to the extent of the sum of:

                                       B-2
<PAGE>

            (a)   the amount, if any, credited under the 1999A Loan Agreement
      Indenture against the obligation of the Company to make payment in respect
      of the corresponding amount of principal of or interest on the 1999A
      Revenue Bonds;

            (b)   the amount, if any, paid by the Company pursuant to the 1999A
      Loan Agreement in respect of such corresponding amount of principal of or
      interest on the 1999A Revenue Bonds; and

            (c)   if Ambac shall have made a payment in respect of such
      corresponding amount of principal of or interest on the 1999A Revenue
      Bonds pursuant to the Policy, the amount, if any, paid by the Company
      pursuant to the Insurance Agreement to reimburse Ambac for such payment.

            Anything in this bond to the contrary notwithstanding, if, at the
time of the Maturity of the bonds of this series, the stated aggregate principal
amount of such bonds then outstanding shall exceed the aggregate principal
amount of 1999_ Revenue Bonds then outstanding, the aggregate principal amount
of such bonds shall be deemed to have been reduced by the amount of such excess.

            The principal hereof may be declared or may become due prior to the
stated maturity date on the conditions, in the manner and at the time set forth
in the Mortgage, upon the occurrence of a Completed Default as in the Mortgage
provided.

            As provided in the Mortgage and subject to certain limitations
therein set forth, this bond or any portion of the principal amount hereof will
be deemed to have been paid if there has been irrevocably deposited with the
Trustee moneys or direct obligations of or obligations guaranteed by the United
States of America, the principal of and interest on which when due, and without
regard to any reinvestment thereof, will provide moneys which, together with
moneys so deposited, will be sufficient to pay when due the principal of and
premium, if any, and interest on this bond when due.

            The Mortgage contains terms, provisions and conditions relating to
the consolidation or merger of the Company with or into, and the conveyance or
other transfer, or lease, of assets to, another Corporation and to the
assumption by such other Corporation, in certain circumstances, of all of the
obligations of the Company under the Mortgage and on the bonds secured thereby.

            This bond is non-transferable except as required to effect transfer
to any successor obligor on the Policy, any such transfer to be made at the
office or agency of the Company in the Borough of Manhattan, The City of New
York, upon surrender and cancellation of this bond, together with a written
instrument of transfer whenever required by the Company duly executed by the
registered owner or by its duly authorized attorney, and, thereupon, a new fully
registered bond of the same series for a like principal amount will be issued to
the transferee in exchange herefor as provided in the Mortgage. The Company and
the Trustee may deem and treat the person in whose name this bond is registered
as the absolute owner hereof for the purpose of receiving payment and for all
other purposes.

                                       B-3
<PAGE>

            In the manner prescribed in the Mortgage, any bonds of this series,
upon surrender thereof for cancellation at the office or agency of the Company
in the Borough of Manhattan, The City of New York, are exchangeable for a like
aggregate principal amount of bonds of the same series of other authorized
denominations.

            No recourse shall be had for the payment of the principal of or
interest on this bond against any incorporator or any past, present or future
subscriber to the capital stock, stockholder, officer or director of the Company
or of any predecessor or successor corporation, as such, either directly or
through the Company or any predecessor or successor corporation, under any rule
of law, statute or constitution or by the enforcement of any assessment or
otherwise, all such liability of incorporators, subscribers, stockholders,
officers and directors being released by the holder or owner hereof by the
acceptance of this bond and being likewise waived and released by the terms of
the Mortgage.

            This bond shall not become obligatory until Citibank, N.A., the
Trustee under the Mortgage, or its successor thereunder, shall have signed the
form of certificate endorsed hereon.

            IN WITNESS WHEREOF, AVISTA CORPORATION has caused this bond to be
signed in its corporate name by its President or one of its Vice Presidents by
his signature or a facsimile thereof, and its corporate seal to be impressed or
imprinted hereon and attested by its Corporate Secretary or one of its Assistant
Corporate Secretaries by his signature or a facsimile thereof.

Dated:

                                        AVISTA CORPORATION

                                        By:_____________________________________

ATTEST:____________________________________

                                       B-4
<PAGE>

                              TRUSTEE'S CERTIFICATE

            This bond is one of the bonds, of the series herein designated,
described or provided for in the within-mentioned Mortgage.

                                        CITIBANK, N.A.
                                        Trustee

                                        By:_____________________________________
                                                     Authorized Officer

                                       B-5
<PAGE>

            FOR VALUE RECEIVED the undersigned hereby sells, assigns and
transfers unto

_______________________________________________________________________

     [please insert social security or other identifying number of assignee]

_______________________________________________________________________

            [please print or typewrite name and address of assignee]

_______________________________________________________________________

the within bond of AVISTA CORPORATION and does hereby irrevocably constitute and
appoint _______________, Attorney, to transfer said bond on the books of the
within-mentioned Company, will full power of substitution in the premises.

Dated: _______________

       __________________

                                        Notice: The signature to this assignment
                                        must correspond with the name as written
                                        upon the face of the bond in every
                                        particular without alteration or
                                        enlargement or any change whatsoever.

                                       B-6

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