UNITED STATES
                      SECURITIES AND EXCHANGE COMMISSION
                           Washington, D.C. 20549

                                FORM 8-K

                             CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934
 Date of Report (date of earliest event reported):  December 22, 2004


                       Westamerica Bancorporation
                       ___________________________
        (Exact name of registrant as specified in its charter)


        California                001-9383                 94-2156203
        __________                ________                 __________
State or other jurisdiction  (Commission File Number)     (IRS Employer
       Of incorporation                                 Identification No.)


           4550 Mangels Boulevard, Fairfield, CA             94585
           _____________________________________             _____
          (Address of principal executive offices)         (Zip Code)


    Registrant's telephone number, including area code:  (707) 863-8000


                                 N/A
                                 ___
     (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to
simultaneously satisfy the filing obligation of the registrant under any
of the following provisions:

    [ ] Written communications pursuant to Rule 425 under the
        Securities Act (17 CFR 230.425)

    [ ] Soliciting material pursuant to Rule 14a-12 under the
        Exchange Act (17 CFR 240.14a-12)

    [ ] Pre-commencement communications pursuant to Rule 14d-2(b)
        under the Exchange Act (17 CFR 240.14d-2(b))

    [ ] Pre-commencement communications pursuant to Rule 13e-4(c)
        under the Exchange Act (17 CFR 240.13e-4(c))








Item 3.03. 	Material Modification to Rights of Security Holders.

         As a precaution to ensure that it continues to be
able to take appropriate action to protect the interests of
Westamerica Bancorporation ("Westamerica" or "Company") and its
shareholders, Westamerica's Board of Directors approved the
amendment of its existing Shareholder Rights Plan on October
28, 2004, to become effective on December 31, 2004 to update
the existing plan and extend its maturity until December 31,
2009.  The new amended plan is very similar in purpose and
effect to the plan as it existed prior to amendment.  It would
help the Board to maximize shareholder value in the event of a
change of control of Westamerica and otherwise to resist
actions that the Board considers likely to injure Westamerica
or its shareholders.

         Integral to the plan is a Rights dividend payable
on shares of Westamerica's Common Stock.  On December 18, 1986,
the Board of Directors of Westamerica declared a dividend
distribution of one Right for each outstanding share of common
stock, no par value (the "Common Stock"), of the Company to
shareholders of record at the close of business on January 20,
1987 (the "Record Date").

         The Rights Agreement, which provides the
description and terms of the Rights, was amended and restated
on September 28, 1989 and on May 25, 1992 the then current
Rights Agent, Chemical Trust Company of California, replaced
the original Rights Agent.  On March 23, 1995, the Company and
Chemical Trust Company of California as Rights Agent, again
amended and restated the Rights Agreement (the "1995 Rights
Agreement").  On November 19, 1999, the then existing rights
agent, ChaseMellon Shareholder Services, LLC (successor in
interest to Chemical Trust Company of California) was replaced
by the current Rights Agent, Harris Trust and Savings Bank, and
the 1995 Rights Agreement was amended and restated (referred to
herein, as amended and restated, as the "1999 Rights
Agreement").  On December 31, 2004, the 1999 Rights Agreement
was amended and restated (referred to herein, as amended and
restated, as the "2004 Rights Agreement") and Computershare
Investor Services, LLC was appointed as Rights Agent. A summary
of the 2004 Rights Agreement is set forth below.

         Except as set forth below, each Right, when
exercisable, entitles the registered holder to purchase from
the Company one share of Common Stock, at a price of $110.00
per share (the "Purchase Price"), subject to adjustment.  The
Rights are not exercisable until the Distribution Date (as
defined below).

         The Rights are currently attached to all Common
Stock certificates representing shares outstanding, and no
separate Right Certificates will be distributed until the
earlier to occur of (i) a public announcement that, without the
prior consent of the Company, a Person or group of affiliated
or associated Persons (an "Acquiring Person") has acquired, or
obtained the right to acquire, beneficial ownership of
securities having 10% or more of the voting power of all
outstanding voting securities of the Company, or (ii) ten days
(unless such date is extended by the Board of Directors)
following the commencement of (or a public announcement of an
intention to make) a tender offer or exchange offer which would
result in any Person or group of related Persons becoming an
Acquiring Person (the earlier of such dates being called the
"Distribution Date").  Until the Distribution Date the Rights
will be evidenced, with respect to any of the Common Stock
certificates outstanding as of the Record Date, by such Common
Stock certificate together with this Amended and Restated
Summary of Rights.  The 2004 Rights Agreement provides that,
until the Distribution Date, the Rights will be transferred
with and only with Common Stock certificates.

         From as soon as practicable after the Record Date
and until the Distribution Date (or earlier redemption or
expiration of the Rights), new Common Stock certificates issued
after the Record Date upon transfer or new issuance of the
Common Stock will contain a notation referring to the
associated Rights.  Until the Distribution Date (or earlier
redemption or expiration of the Rights), the surrender for
transfer of any certificates for Common Stock outstanding as of
the Record Date (with or without this Amended and Restated
Summary of Rights attached) will also constitute the transfer
of the Rights associated with the Common Stock represented by
such certificate.  As soon as practicable following the
Distribution Date, Westamerica will issue certificates
evidencing the Rights ("Rights Certificates"), and the Rights
will become exercisable and separately tradable.

         The Rights will expire on the earliest of
(i) December 31, 2009, (ii) consummation of a merger
transaction with a Person or group who acquired Common Stock
pursuant to a Permitted Offer (as defined below), and is
offering in the merger the same price per share and form of
consideration paid in the Permitted Offer, or (iii) redemption
of the Rights by the Company as described below.

         The Purchase Price payable, and the number of
shares of the Common Stock or other securities or property
issuable, upon exercise of the Rights are subject to adjustment
from time to time to prevent dilution (i) in the event of a
stock dividend on, or a subdivision, combination or
reclassification of the Common Stock, (ii) upon the grant to
holders of the Common Stock of certain rights or warrants to
subscribe for Common Stock, certain convertible securities or
securities having the same or more favorable rights, privileges
and preferences as the Common Stock at less than the current
market price of the Common Stock or (iii) upon the distribution
to holders of the Common Stock of evidences of indebtedness or
assets (excluding regular quarterly cash dividends out of
earnings or retained earnings and dividends payable in Common
Stock) or of subscription rights or warrants (other than those
referred to above).

         In the event that, after the first date of public
announcement by the Company or an Acquiring Person that an
Acquiring Person has become such, (i) the Company is acquired
in a merger or other business combination transaction in which
the Common Stock is exchanged or changed, (ii) any bank
subsidiary of the Company is involved in a merger or other
business combination transaction or (iii) 50% or more of its
assets or earning power are sold (in one transaction or a
series of transactions), proper provision shall be made so that
each holder of a Right (other than such Acquiring Person) shall
thereafter have the right to receive, upon the exercise thereof
at the then current exercise price of the Right, that number of
shares of common stock of the surviving or resulting Person in
the merger or business combination transaction or the Person
acquiring the greatest portion of the assets, as appropriate,
or, in either case, its publicly traded parent company or
affiliate, which at the time of such transaction would have a
market value of two times the exercise price of the Right (such
right being called the "Merger Right").

         In the event that a Person becomes the beneficial
owner of securities having 10% or more of the voting power of
all then outstanding voting securities of the Company (unless
pursuant to a tender offer or exchange offer for all
outstanding shares of Common Stock at a price and on terms
determined by at least a majority of the members of the Board
of Directors who are not officers of the Company to be both
adequate and otherwise in the best interests of the Company and
its shareholders (a "Permitted Offer")), proper provision shall
be made so that each holder of a Right will for a 60-day period
thereafter have the right to receive upon exercise that number
of shares of Common Stock having a market value of two times
the exercise price of the Right, to the extent available, and
then (after all authorized and unreserved shares of Common
Stock have been issued) a common stock equivalent (such as
Preferred Stock or another equity security with at least the
same economic value as the Common Stock) having a market value
of two times the exercise price of the Right, with Common Stock
to the extent available being issued first (such right being
called the "Subscription Right").  The holder of a Right will
continue to have the Merger Right whether or not such holder
exercises the Subscription Right.  Upon the occurrence of any
of the events giving rise to the exercisability of the Merger
Right or the Subscription Right, any Rights that are or were at
any time after the Distribution Date owned by an Acquiring
Person shall immediately become null and void.

         With certain exceptions, no adjustments in the
Purchase Price will be required until cumulative adjustments
require an adjustment of at least 1% in such Purchase Price.
No fractions of shares will be issued and, in lieu thereof, an
adjustment in cash will be made based on the market price of
the Common Stock on the last trading date prior to the date of
exercise.

         At any time prior to the earlier to occur of (i) a
Person becoming an Acquiring Person or (ii) the expiration of
the Rights, the Company may redeem the Rights in whole, but not
in part, at a price of $.001 per Right (the "Redemption
Price"), which redemption shall be effective upon the action of
the Board of Directors.  Additionally, the Company may
thereafter redeem the then outstanding Rights in whole, but not
in part, at the Redemption Price (i) provided that such
redemption is incidental to a merger or other business
combination transaction or series of transactions involving the
Company but not involving an Acquiring Person or certain
related Persons or (ii) following an event giving rise to, and
the expiration of the exercise period for, the Subscription
Right if and for as long as an Acquiring Person beneficially
owns securities representing less than 10% of the voting power
of the Company's voting securities and at the time of
redemption there are no other persons who are Acquiring
Persons.  The redemption of Rights described in the preceding
sentence shall be effective only as of such time when the
Subscription Right is not exercisable, and in any event, only
after 10 Business Days' prior notice.

         Subject to applicable law, the Board of Directors,
at its option, may at any time after a Person becomes an
Acquiring Person (but not after the acquisition by such Person
of 50% or more of the outstanding Common Stock), exchange all
or part of the then outstanding and exercisable rights (except
for Rights which have become void) for shares of Common Stock
equivalent to one share of Common Stock per Right or,
alternatively, for substitute consideration consisting of cash,
securities of the Company or other assets (or any combination
thereof).

         Fractional shares of Common Stock will be issuable;
however, the Company may elect to distribute depositary
receipts in lieu of such fractional shares.  In lieu of
fractional shares an adjustment in cash may be made based on
the market price of the Common Stock on the last trading date
prior to the date of exercise.

         Until a Right is exercised, the holder thereof, as
such, will have no rights as a shareholder of the Company,
including, without limitation, the right to vote or to receive
dividends.

         A copy of the 2004 Rights Agreement has been filed
with the Securities and Exchange Commission as an Exhibit to an
Amendment to a Registration Statement on Form 8-A.  A copy of
the 2004 Rights Agreement is available free of charge from the
Company.  This summary description of the Rights does not
purport to be complete and is qualified in its entirety by
reference to the 2004 Rights Agreement, filed as an exhibit to
this report, which is incorporated herein by reference.

Item 9.01.	Financial Statements and Exhibits.

(c)	Exhibits. The list of exhibits called for by this
Item is incorporated by reference to the Exhibit Index to
this report.









SIGNATURES

Pursuant to the requirements of the Securities Exchange
Act of 1934, the registrant has duly caused this report
to be signed on its behalf by the undersigned hereunto
duly authorized.


Dated: December 22, 2004        Westamerica Bancorporation


                                By  /s/   DENNIS R. HANSEN
                                ____________________________________
                                Dennis R. Hansen
                                Senior Vice President and Controller











                     EXHIBIT INDEX

4.	Amended and Restated Rights Agreement dated as of
      December 31, 2004 between Westamerica Bancorporation and
      Computershare Investor Services, LLC, which includes as
      Exhibit A the form of Rights Certificate (incorporated by
      reference to Exhibit 99 to Amendment No. 4 to
      Registration Statement on Form 8-A of Westamerica
      Bancorporation dated December 22, 2004).