13G Filing: Blue Mountain Capital and Avista Healthcare Public Acquisiton Corp (AHPA)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No. 1)*

AVISTA
HEALTHCARE PUBLIC ACQUISITION CORP.

(Name of Issuer)

Class A Ordinary Share, par value $0.0001 per share

(Title of Class of Securities)

G0726L109

(CUSIP Number)

November 28, 2017

(Date of Event which Requires Filing of this Statement)

Check the appropriate box to
designate the rule pursuant to which this Schedule is filed:

☐	Rule 13d-1(b)

☒	Rule 13d-1(c)

☐	Rule 13d-1(d)

*	The remainder of this cover page shall be filled out for a reporting persons initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be
deemed to be filed for the purpose of Section 18 of the Securities Exchange Act of 1934 (Act) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the
Act (however, see the Notes).

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CUSIP No. G0726L109		13G		Page 2 of 6 Pages

1.		NAMES OF REPORTING PERSONS BlueMountain Capital Management, LLC
2.		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (see instructions) (a)  ☐        (b)  ☒
3.		SEC USE ONLY
4.		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware, United States of America
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH				5.		SOLE VOTING POWER 0
				6.		SHARED VOTING POWER 2,040,718
				7.		SOLE DISPOSITIVE POWER 0
				8.		SHARED DISPOSITIVE POWER 2,040,718
9.		AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 2,040,718
10.		CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (see instructions) ☐
11.		PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 6.6% (1)
12.		TYPE OF REPORTING PERSON (see instructions) IA

(1)

The percentage set forth in Row 11 of this Cover Page is based on the 31,000,000 shares of Ordinary Shares (as defined herein) of the Issuer (as defined herein) outstanding as of November 14, 2017, as reported on the Issuers Form 10-Q filed with the Securities and Exchange Commission on November 14, 2017 (Form 10-Q).

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CUSIP No. G0726L109		13G		Page 3 of 6 Pages

1.		NAMES OF REPORTING PERSONS Blue Mountain Credit Alternatives Master Fund L.P.
2.		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (see instructions) (a)  ☐        (b)  ☒
3.		SEC USE ONLY
4.		CITIZENSHIP OR PLACE OF ORGANIZATION Cayman Islands
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH				5.		SOLE VOTING POWER 0
				6.		SHARED VOTING POWER 0
				7.		SOLE DISPOSITIVE POWER 0
				8.		SHARED DISPOSITIVE POWER 0
9.		AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 0
10.		CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (see instructions) ☐
11.		PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 0.0% (1)
12.		TYPE OF REPORTING PERSON (see instructions) PN

(1)	The percentage set forth in Row 11 of this Cover Page is based on the 31,000,000 shares of Ordinary Shares of the Issuer outstanding as of November 14, 2017, as reported on Form 10-Q.

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CUSIP No. G0726L109		13G		Page 4 of 6 Pages

Item 1.

(a)

Name of Issuer

Avista Healthcare Public Acquisition Corp.

(b)

Address of Issuers principal executive offices

65 East 55th Street, 18th Floor,
New York, New York 10022

Item 2.

(a)

Name of person filing

This Amendment No. 1 (this Amendment) to
the Schedule 13G filed on October 19, 2016 is being filed on behalf of BlueMountain Capital Management, LLC (BMCM) and Blue Mountain Credit Alternatives Master Fund L.P. (BMCA) with respect to the shares of
Class A Ordinary Shares, $0.0001 par value per share (the Ordinary Shares), of Avista Healthcare Public Acquisition Corp., a Cayman Islands exempted company (the Issuer).

BMCM, which is the beneficial owner of 1,623,446 shares of Ordinary Shares, acts as investment manager to, and exercises investment discretion
with respect to the following beneficial owners of Ordinary Shares (each, a BlueMountain Fund):

(i)

BlueMountain Foinaven Master Fund L.P., a Cayman Islands exempted limited partnership, with respect to the 86,800 shares of Ordinary Shares directly owned by it;

(ii)

BlueMountain Montenvers Master Fund SCA SICAV-SIF, an investment company with variable capital organized as a specialized investment fund in the form of a corporate partnership limited by shares under the laws of Luxembourg, with respect to the 187,509 shares of Ordinary Shares directly owned by it;

(iii)

BlueMountain Guadalupe Peak Fund L.P., a Delaware limited partnership, with respect to the 61,600 shares of Ordinary Shares directly owned by it; and

(iv)

BlueMountain Kicking Horse Fund L.P., a Cayman Islands exempted limited partnership, with respect to the 81,363 shares of Ordinary Shares directly owned by it.

The filing of this statement should not be construed as an admission that BMCM is, for the purpose of Section 13 of the Act, the
beneficial owner of the Ordinary Shares owned by the BlueMountain Funds.

(b)

Address or principal business office or, if none, residence

280 Park Avenue, 12th
Floor, New York, New York 10017

(c)

Citizenship

See Row 4 of each Cover Page.

(d)

Title of class of securities

Class A Ordinary Shares, par value $0.0001 per share

(e)

CUSIP No.

G0726L109

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:

(a)

☐ Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).

(b)

☐ Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).

(c)

☐ Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).

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CUSIP No. G0726L109		13G		Page 5 of 6 Pages

(d)

☐ Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8).

(e)

☐ An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);

(f)

☐ An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);

(g)

☐ A parent holding company or control person in accordance with §240.13d-1(b)(1)(ii)(G);

(h)

☐ A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

☐ A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

(j)

☐ Group, in accordance with §240.13d-1(b)(1)(ii)(K).

Item 4. Ownership.

The information required by
Items 4(a)-(c) is set forth in Rows 5-11 of each Cover Page and is incorporated herein by reference.

BMCM
expressly declares that this filing shall not be construed as an admission that it is, for the purposes of Sections 13(d) or 13(g) of the Act, the beneficial owner of the securities owned by the BlueMountain Funds.

Item 5. Ownership of 5 Percent or Less of a Class.

This Amendment constitutes an exit filing for BMCA.

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 5 percent of the class of securities, check the following  ☐.

Item 6. Ownership of More than 5 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, other than activities solely in connection with a nomination under § 240.14a-11.

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CUSIP No. G0726L109		13G		Page 6 of 6 Pages

SIGNATURES

After reasonable inquiry and to the best of each of the undersigneds knowledge and belief, each of the undersigned certifies that the information set
forth in this statement is true, complete and correct.

DATED: December 8, 2017

BLUEMOUNTAIN CAPITAL MANAGEMENT, LLC

By:		/s/ Eric M. Albert
Eric M. Albert, Chief Compliance Officer

BLUE MOUNTAIN CREDIT ALTERNATIVES MASTER FUND L.P.

By: Blue Mountain CA Master Fund GP, Ltd.

By:		/s/ Andrew Feldstein
Andrew Feldstein, Director