Exhibit 5(a)

                          [Letterhead of Avista Corp.]

December 11, 2006

Avista Corporation
1411 East Mission Avenue
Spokane, WA 99202

Ladies and Gentlemen:

      I am a Senior Vice President, General Counsel & Chief Compliance Officer
of Avista Corporation, a Washington corporation (the "Company"), and am acting
as counsel to the Company in connection with the filing by the Company of a
Registration Statement on Form S-3 (the "Registration Statement") under the
Securities Act of 1933, as amended (the "Act"), relating to the registration of
(1) secured debt securities (the "Secured Debt Securities") under the Mortgage
and Deed of Trust, dated as of June 1, 1939, as amended and supplemented (the
"Mortgage"), from the Company to Citibank, N.A., as trustee, (2) unsecured debt
securities (the "Unsecured Debt Securities", and, together with the Secured Debt
Securities, the "Debt Securities") under the Indenture, dated as of April 1,
1998 (the "Indenture"), from the Company to The Bank of New York, as successor
trustee, (3) shares of the Company's Preferred Stock, cumulative, no par value
(the "New Preferred Shares"), (4) shares of the Company's common stock, no par
value (the "New Common Shares"), to be issued and sold from time to time by the
Company in one or more public offerings. The New Common Shares will be offered
and issued together with the related preferred share purchase rights (the "New
Rights") in accordance with the Rights Agreement, dated as of November 15, 1999
(the "Rights Agreement"), between the Company and The Bank of New York, as
rights agent.

      I have examined (1) the Registration Statement, (2) the Company's Restated
Articles of Incorporation, as amended, and By-Laws, (3) a Certificate of
Existence/Authorization with respect to the Company issued by the Secretary of
State of the State of Washington, (4) the Mortgage, (5) the Indenture, (6) the
Rights Agreement, (7) orders of the Washington Utilities and Transportation
Commission (the "WUTC"), the Idaho Public Utilities Commission (the "IPUC") and
the Public Utility Commission of Oregon (the "OPUC") authorizing the issuance
and sale by the Company of the New Common Shares, as well as the exemptive order
of the Public Service Commission of the State of Montana disclaiming
jurisdiction over the issuance of securities and the creation of liens by the
Company and (8) various corporate records and other documents relating to the
authorization of the issuance and sale by the Company of securities. I have also
examined such other documents and satisfied myself as to such other matters as I
have deemed necessary in order to deliver this letter.



Avista Corporation
December 11, 2006
Page 2

      On the basis of the foregoing, and subject to the qualifications
hereinafter expressed, I am of the opinion that:

            (1) when (a) the WUTC, the IPUC and the OPUC have issued appropriate
      orders authorizing the issuance and sale by the Company of the Debt
      Securities and (b) the Debt Securities have been issued, sold and paid for
      as contemplated in the Registration Statement, the Debt Securities will be
      legally issued and will be binding obligations of the Company, except as
      limited by laws and principles of equity relating to or affecting
      generally the enforcement of mortgagees' and other creditors' rights
      including, without limitation, bankruptcy and insolvency laws (such laws
      and principles of equity being hereinafter called, collectively, the
      "Exceptions");

            (2) when (a) the WUTC, the IPUC and the OPUC have issued appropriate
      orders authorizing the issuance and sale by the Company of the New
      Preferred Shares and (b) the New Preferred Shares have been issued, sold
      and paid for as contemplated in the Registration Statement, the New
      Preferred Shares will be legally issued, fully paid and non-assessable;
      and

            (3) when the New Common Shares have been issued, sold and paid for
      as contemplated in the Registration Statement, the New Common Shares will
      be legally issued, fully paid and non-assessable and the New Rights will
      be legally issued and binding obligations, except as may be limited by the
      Exceptions.

      It is also my opinion that Section 23B.06.240 of the Washington Business
Corporation Act permits Washington corporations to enter into shareholder rights
plans, such as the Rights Agreement, and to issue rights thereunder, such as the
New Rights. However, I am not aware of any court decisions applying Washington
law that address the validity of actions taken by the board of directors of a
Washington corporation in authorizing a shareholder rights plan or the issuance
of rights thereunder.

      In my view, it is reasonable to assume, and I do assume, that a court
applying the law of the State of Washington, when presented with questions
concerning matters such as the authorization and issuance of the New Rights,
after giving effect to the "business judgment rule" under Washington statutory
and case law, most likely would look to and apply the corporation law of the
State of Delaware for guidance and authority. Accordingly, my opinion relating
to the legal issuance of the New Rights is based, in part, upon such assumption.

      For the purposes of the opinions expressed above, I have assumed that the
Debt Securities, the New Preferred Shares, the New Common Shares and the New
Rights will be issued and sold in compliance with the orders of the WUTC, the
IPUC and the OPUC authorizing the issuance and sale by the Company of such
securities and with the authorization of the Company's Board of Directors.



Avista Corporation
December 11, 2006
Page 3

      I am a member of the Bar of the State of Washington. To the extent that
the opinions expressed above relate to or are dependent upon matters governed by
the law of the State of Idaho, Montana or Oregon, I have relied upon advice
rendered to me by other counsel to the Company admitted to practice in such
State whom I consider competent. In addition, to the extent that the opinions
expressed above relate to or are dependent upon matters governed by the federal
securities laws, the Federal Power Act, as amended, or the Public Utility
Holding Company Act of 2005, I have relied upon the opinions expressed in the
letter of even date herewith of Dewey Ballantine LLP, counsel to the Company,
which is being filed as Exhibit 5(b) to the Registration Statement, and my
opinions are subject to the same assumptions, limitations and qualifications
with respect to such matters as are set forth in such letter. I do not herein
express any opinion as to the law of the State of New York.

      Dewey Ballantine LLP is hereby authorized to rely upon the opinions
expressed in this letter as to all matters governed by the law of the State of
Washington, Idaho, Montana or Oregon.

      I hereby consent to the filing of this letter as Exhibit 5(a) to the
Registration Statement and to the references to me, as counsel, in the
Registration Statement and in the prospectus contained therein. In giving the
foregoing consent, I do not admit that I am within the category of persons whose
consent is required under Section 7 of the Act or the rules and regulations
promulgated thereunder.

Very truly yours,

/s/  Marian M. Durkin
---------------------------------------
Marian M. Durkin
Senior Vice President, General Counsel
& Chief Compliance Officer