UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

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Rule 13d-1(b)

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Rule 13d-1(c)

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Rule 13d-1(d)

CUSIP No.  689648103

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Cascade Investment, L.L.C.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

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3.

SEC Use Only

4.

Citizenship or Place of Organization
State of Washington

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
1,547,799

6.

Shared Voting Power
-0-

7.

Sole Dispositive Power
1,547,799

8.

Shared Dispositive Power
-0-

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
1,547,799

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
6.0%

12.

Type of Reporting Person (See Instructions)
OO

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
William H. Gates III

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
United States of America

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
1,547,799

6.

Shared Voting Power
-0-

7.

Sole Dispositive Power
1,547,799

8.

Shared Dispositive Power
-0-

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
1,547,799

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
6.0%

12.

Type of Reporting Person (See Instructions)
IN

Item 1.

(a)

Name of Issuer
Otter Tail Corporation (the “Issuer”)

(b)

Address of Issuer’s Principal Executive Offices
215 South Cascade Street, Box 496
Fergus Falls, MN, 56538-0496

Item 2.

(a)

Name of Person Filing
Cascade Investment, L.L.C. (“Cascade”) and William H. Gates III (“Gates”)

(b)

Address of Principal Business Office or, if none, Residence
Cascade – 2365 Carillon Point, Kirkland, Washington  98033

Gates – One Microsoft Way, Redmond, Washington  98052

(c)

Citizenship
Cascade is a limited liability company organized under the laws of the State of Washington.

Gates is a citizen of the United States of America.

(d)

Title of Class of Securities
Common Stock, par value $5.00 per share (“Common Stock”)

(e)

CUSIP Number
689648103

Item 3.

If this statement is filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

Not Applicable

Item 4.

Ownership

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

(a)

Amount beneficially owned:

1,547,799*

(b)

Percent of class:

6.0%

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote

1,547,799*

(ii)

Shared power to vote or to direct the vote

-0-

(iii)

Sole power to dispose or to direct the disposition of

1,547,799*

(iv)

Shared power to dispose or to direct the disposition of

-0-

*  All Common Stock held by Cascade may be deemed to be beneficially owned by William H. Gates III as the sole member of Cascade.  Michael Larson, the manager and executive officer of Cascade, has voting and investment power with respect to the Common Stock held by Cascade.  Mr. Larson disclaims any beneficial ownership of the Common Stock beneficially owned by Cascade and Mr. Gates.

Item 5.

Ownership of Five Percent or Less of a Class

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following  o.

Not Applicable

Item 6.

Ownership of More than Five Percent on Behalf of Another Person

Not Applicable

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person

Not Applicable

Item 8.

Identification and Classification of Members of the Group

Not Applicable

Item 9.

Notice of Dissolution of Group

Not Applicable

Item 10.

Certification

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

Dated: February 17, 2004

CASCADE INVESTMENT, L.L.C.

By

/s/ Michael Larson

Name:

Michael Larson

Title:

Manager

WILLIAM H. GATES III

By

/s/ Michael Larson

Name:

Michael Larson*

Title:

Attorney-in-fact

DATED: February 17, 2004

CASCADE INVESTMENT, L.L.C.

By

/s/ Michael Larson

Name:

Michael Larson

Title

Manager

WILLIAM H. GATES III

By

/s/ Michael Larson

Name:

Michael Larson*

Title:

Attorney-in-fact