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                              January 30, 2024

       Steven Burdick
       Executive Vice President and Chief Financial Officer
       Tetra Tech, Inc.
       3475 East Foothill Boulevard
       Pasadena, CA 91107

                                                        Re: Tetra Tech, Inc.
                                                            Form 10-K for 
Fiscal Year Ended October 1, 2023
                                                            Form 8-K Furnished 
November 15, 2023
                                                            File No. 000-19655

       Dear Steven Burdick:

              We have limited our review of your filing to the financial 
statements and related
       disclosures and have the following comment(s).

              Please respond to this letter within ten business days by 
providing the requested
       information or advise us as soon as possible when you will respond. If 
you do not believe a
       comment applies to your facts and circumstances, please tell us why in 
your response.

                                                        After reviewing your 
response to this letter, we may have additional comments.

       Form 10-K for Fiscal Year Ended October 1, 2023

       Management's Discussion and Analysis of Results of Operations and 
Financial Condition
       Results of Operations, page 35

   1.                                                   A significant portion 
of your results of operations disclosure is dedicated to stating, in
                                                        narrative text form, 
dollar and percentage changes in accounts that are included in
                                                        accompanying tables. In 
addition, while you discuss certain factors to which changes are
                                                        attributable, you do 
not quantify certain of these factors nor analyze the underlying
                                                        business reasons for 
the changes. For example, you state the increase in GSG revenue in
                                                        2023 reflect higher 
U.S. state and local government activities related to digital water and
                                                        U.S. federal programs, 
partially offset by lower disaster response revenue, but you do not
                                                        quantify these factors 
nor analyze the underlying reasons for the change. As such, please
                                                        consider revising your 
disclosure by:

                                                              relying on tables 
to present dollar and percentage changes in accounts, rather than
                                                            including and 
repeating such information in narrative text form;
 Steven Burdick
Tetra Tech, Inc.
January 30, 2024
Page 2
                using additional tables to list, quantify, and sum all of the 
material individual factors
              to which changes in accounts are attributable;
                refocusing the narrative text portion of the disclosure on 
analysis of the underlying
              business reasons for the individual factors in the tables above;
                ensuring that all material factors are quantified and analyzed; 
and
                quantifying the effects of changes in price, volume, and 
acquisitions on revenues and
              expense categories, where appropriate.

         In addition, please revise to quantify the portion of the $600 million 
of revenue growth
         from the RPS Group acquisition for each revenue category and discuss 
and analyze other
         costs of revenue directly. Refer to the introductory paragraph to Item 
303 of Regulation S-
         K.
Financial Condition, Liquidity and Capital Resources
Operating Activities, page 40

2.       Please revise your discussion and analysis of cash flows to analyze 
the underlying reasons
         for material changes, as well as on their reasonably likely impact on 
future cash flows and
         cash management decisions. Where reported amounts of cash provided and 
used by
         operations, investing activities or financing have been consistent, if 
the underlying sources
         of those cash flows have materially varied, analysis of that 
variability should be provided.
         Please note that merely citing changes in results, working capital 
items, and noncash items
         reported in the statement of cash flows may not provide a sufficient 
basis to understand
         changes in operating cash between periods. Refer to section IV.B and 
B.1 of Release No.
         33-8350 for guidance.
Earnings Release on Form 8-K Furnished November 15, 2023

Investor Presentation for Earnings Call Held on November 16, 2023
EBITDA Margin Trend on U.S. and International Reporting Basis
Reconciliation Summary for EBITDA, IFRS and Net Service Revenue (NSR)

3.     We note you present non-IFRS measures in the PowerPoint slides furnished 
in
       conjunction with your earnings call held on November 16, 2023 for the 
fourth quarter
       ended October 1, 2023. Please present the most directly comparable GAAP 
or IFRS
       measure for these non-IFRS measures and reconcile the non-IFRS measures 
to the most
       directly comparable GAAP or IFRS measures. In addition, please explain 
the purpose of
       presenting the IFRS adjusted measures on a comparative basis with the 
non-GAAP
       measures for Adjusted EBITDA Margin, Net Service Revenue, and EBITDA 
margin as a
FirstName LastNameSteven Burdick
       percentage of NSR and why this is appropriate. Refer to Items 100(a)(1) 
and 100(a)(2)
Comapany   NameTetra
       and Question     Tech,ofInc.
                     103.02      the Compliance and Disclosure Interpretation 
on Non-GAAP
       Financial Measures.
January 30, 2024 Page 2
FirstName LastName
 Steven Burdick
FirstName
Tetra Tech,LastNameSteven Burdick
            Inc.
Comapany
January 30,NameTetra
            2024     Tech, Inc.
January
Page 3 30, 2024 Page 3
FirstName LastName
       In closing, we remind you that the company and its management are 
responsible for the
accuracy and adequacy of their disclosures, notwithstanding any review, 
comments, action or
absence of action by the staff.

       Please contact Robert Shapiro at 202-551-3273 or Lyn Shenk at 
202-551-3380 with any
questions.



                                                          Sincerely,

                                                          Division of 
Corporation Finance
                                                          Office of Trade & 
Services