Amendment: SEC Form SCHEDULE 13D/A filed by TransAlta Corporation

Item 4 of the original Schedule 13D is hereby supplemented as follows: The Purchaser Reporting Persons disposed of an aggregate 8,600,000 Common Shares in a block trade pursuant to Regulation S under the U.S. Securities Act of 1933, as amended, for aggregate cash proceeds of approximately C$168,990,000 (excluding brokerage commission), at a price of C$19.65 per Common Share. The disposition of the Common Shares reported in this Amendment No. 6 more closely aligns the Reporting Persons' aggregate share ownership with certain thresholds under the Investment Agreement. Although the Reporting Persons have no current specific plan or proposal for further dispositions of the Common Shares, the Reporting Persons also may, at any time and from time to time, subject to compliance at all relevant times with the Investment Agreement, A&R Margin Loan Agreement and regulatory requirements and applicable securities laws, terminate in whole or in part, dispose of or distribute some or all of their Common Shares or such other securities they own or may subsequently acquire, depending on various factors, including the price of the Common Shares, terms and conditions applicable to any potential transaction, liquidity and diversification objectives of the Reporting Persons and such other factors that the Reporting Persons deem relevant at any time or from time to time.

Sections (a) and (b) of Item 5 of the original Schedule 13D are hereby amended and restated as follows: The aggregate number and percentage of Common Shares held by the Reporting Persons to which this Amendment No. 6 relates is 26,923,345 Common Shares, constituting approximately 9.0% of the Issuer's currently outstanding Common Shares. The percentage of Common Shares of the Issuer in this Item 5 is based on an aggregate 298,500,000 Common Shares of the Issuer outstanding as of September 30, 2024 based on Issuer's 2024 Q3 Interim Report, filed on Form 6-K dated November 5, 2024. (i) Brookfield (a) Brookfield may be deemed the beneficial owner of 26,923,345 Common Shares, constituting a percentage of approximately 9.0% (b) Sole voting power to vote or direct vote: 0 Common Shares Shared voting power to vote or direct vote: 26,923,345 Common Shares Sole power to dispose or direct the disposition: 0 Common Shares Shared power to dispose or direct the disposition: 26,923,345 Common Shares (ii) BAM Partnership (a) BAM Partnership may be deemed the beneficial owner of 26,923,345 Common Shares, constituting a percentage of approximately 9.0% (b) Sole voting power to vote or direct vote: 0 Common Shares Shared voting power to vote or direct vote: 26,923,345 Common Shares Sole power to dispose or direct the disposition: 0 Common Shares Shared power to dispose or direct the disposition: 26,923,345 Common Shares (iii) Eagle Canada (a) Eagle Canada may be deemed the beneficial owner of 10,316,598 Common Shares, constituting a percentage of approximately 3.5% (b) Sole voting power to vote or direct vote: 0 Common Shares Shared voting power to vote or direct vote: 10,316,598 Common Shares Sole power to dispose or direct the disposition: 0 Common Shares Shared power to dispose or direct the disposition: 10,316,598 Common Shares (iv) BIF IV Eagle (a) BIF IV Eagle may be deemed the beneficial owner of 16,606,747 Common Shares, constituting a percentage of approximately 5.6% (b) Sole voting power to vote or direct vote: 0 Common Shares Shared voting power to vote or direct vote: 16,606,747 Common Shares Sole power to dispose or direct the disposition: 0 Common Shares Shared power to dispose or direct the disposition: 16,606,747 Common Shares (v) BIF IV LTIP (a) BIF IV LTIP may be deemed the beneficial owner of 16,606,747 Common Shares, constituting a percentage of approximately 5.6% (b) Sole voting power to vote or direct vote: 0 Common Shares Shared voting power to vote or direct vote: 16,606,747 Common Shares Sole power to dispose or direct the disposition: 0 Common Shares Shared power to dispose or direct the disposition: 16,606,747 Common Shares (vi) BIF IV Cdn (a) BIF IV Cdn may be deemed the beneficial owner of 26,923,345 Common Shares, constituting a percentage of approximately 9.0% (b) Sole voting power to vote or direct vote: 0 Common Shares Shared voting power to vote or direct vote: 26,923,345 Common Shares Sole power to dispose or direct the disposition: 0 Common Shares Shared power to dispose or direct the disposition: 26,923,345 Common Shares (vii) BIF IV Cdn GP (a) BIF IV Cdn GP may be deemed the beneficial owner of 26,923,345 Common Shares, constituting a percentage of approximately 9.0% (b) Sole voting power to vote or direct vote: 0 Common Shares Shared voting power to vote or direct vote: 26,923,345 Common Shares Sole power to dispose or direct the disposition: 0 Common Shares Shared power to dispose or direct the disposition: 26,923,345 Common Shares (viii) BIF IV Cdn GP Ltd. (a) BIF IV Cdn GP Ltd. may be deemed the beneficial owner of 26,923,345 Common Shares, constituting a percentage of approximately 9.0% (b) Sole voting power to vote or direct vote: 0 Common Shares Shared voting power to vote or direct vote: 26,923,345 Common Shares Sole power to dispose or direct the disposition: 0 Common Shares Shared power to dispose or direct the disposition: 26,923,345 Common Shares (ix) BIGL (a) BIGL may be deemed the beneficial owner of 26,923,345 Common Shares, constituting a percentage of approximately 9.0% (b) Sole voting power to vote or direct vote: 0 Common Shares Shared voting power to vote or direct vote: 26,923,345 Common Shares Sole power to dispose or direct the disposition: 0 Common Shares Shared power to dispose or direct the disposition: 26,923,345 Common Shares (x) BIG Timber Holdings L.P. (a) BIG Timber Holdings L.P. may be deemed the beneficial owner of 26,923,345 Common Shares, constituting a percentage of approximately 9.0% (b) Sole voting power to vote or direct vote: 0 Common Shares Shared voting power to vote or direct vote: 26,923,345 Common Shares Sole power to dispose or direct the disposition: 0 Common Shares Shared power to dispose or direct the disposition: 26,923,345 Common Shares

The information set forth in Item 5(a) of this Amendment No. 6 is hereby incorporated herein by reference.

Section (c) of Item 5 of the original Schedule 13D is hereby amended and restated as follows: The transactions described in Item 4 and Schedule V filed herewith, which is incorporated herein by reference, describes all of the transactions in Common Shares of the Issuer that were effected in the past 60 days by the Reporting Persons.

Exhibit 99.1 Schedule I Exhibit 99.2 Schedule II Exhibit 99.3 Schedule III Exhibit 99.4 Schedule IV Exhibit 99.5 Schedule V