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                                                                     Exhibit 5.1

                       [SCHIFF HARDIN & WAITE LETTERHEAD]




                                  June 14, 2001



CIB Marine Bancshares, Inc.
N27 W24025 Paul Court
Pewaukee, Wisconsin 53072


                  RE:      REGISTRATION STATEMENT ON FORM S-4

Ladies and Gentlemen:

                  We have acted as counsel to CIB Marine Bancshares, Inc., a
Wisconsin corporation ("CIB"), in connection with its filing of a Registration
Statement on Form S-4 (the "Registration Statement") under the Securities Act of
1933, as amended (the "Securities Act"), with respect to the registration of
shares of Common Stock of CIB, $1.00 par value (the "CIB Common Shares"), to be
issued pursuant to the Agreement and Plan of Reorganization dated as of March 6,
2001, among CIB, Citrus Financial Services, Inc. ("Citrus") and Citrus Bank,
N.A. (the "Reorganization Agreement.")

                  In connection with our opinion, we have examined the
Registration Statement, including the exhibits thereto, and such other
documents, corporate records and instruments, and have examined such laws and
regulations, as we have deemed necessary for the purposes of this opinion. In
such examination, we have assumed the genuineness of all signatures, the
authenticity of all documents submitted to us as originals, the conformity to
the original documents of all documents submitted to us as copies and the
authenticity of the originals of such latter documents.

                  On the basis of such examination, we are of the opinion that
the CIB Marine Shares have been duly authorized, and, when the Registration
Statement, as it may be amended, has become effective under the Securities Act,
any applicable state securities or Blue Sky laws have been complied with, and
the certificates representing the CIB Common Shares are duly executed,
countersigned, registered and delivered in exchange for Citrus common shares as
provided in the Reorganization Agreement, the CIB Common Shares will be validly
issued, fully paid, and nonassessable (except with



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CIB Marine Bancshares, Inc.
June 14, 2001
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respect to wage claims of, or other debts owing to, employees of CIB for
services performed, but not exceeding six months' service in any one case, as
provided in Section 180.0622(2)(b) of the Wisconsin Statutes and as such section
may be interpreted by a court of law.)

                  The foregoing opinion is limited to the Wisconsin Business
Corporation Law, and we express no opinion as to any other laws or the laws of
any other jurisdiction.

                  We hereby consent to the filing of this opinion as Exhibit 5.1
to the Registration Statement and to the reference to us under the caption
"Legal Matters" in the proxy statement/prospectus contained in the Registration
Statement.

                                               Very truly yours,

                                               SCHIFF HARDIN & WAITE


                                               By: /s/ Christopher J. Zinski
                                                  -----------------------------
                                                  Christopher J. Zinski

CJZ/lk