Other Events. On July 29, 2026, Tetra Tech announced that its Board of Directors has declared a $0.072 per share quarterly cash dividend. The dividend is payable on August 27, 2026 to stockholders of record as of the close of business on August 13, 2026.

Results of Operations and Financial Condition. On July 29, 2026, Tetra Tech, Inc. (“Tetra Tech”) reported its financial results for the third fiscal quarter ended June 28, 2026. A copy of the press release is attached to this report as Exhibit 99.1. Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended.

Other Events. On April 29, 2026, Tetra Tech announced that its Board of Directors has declared a $0.072 per share quarterly cash dividend. The dividend is payable on June 2, 2026 to stockholders of record as of the close of business on May 14, 2026.

Results of Operations and Financial Condition. On April 29, 2026, Tetra Tech, Inc. (“Tetra Tech”) reported its financial results for the second fiscal quarter ended March 29, 2026. A copy of the press release is attached to this report as Exhibit 99.1. Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended.

Director — Eric W. Thornburg: Eric W. Thornburg was appointed to the Board of Directors.

Annual board election with no specific departures or appointments mentioned.

Other Events. On January 28, 2026, Tetra Tech announced that its Board of Directors has declared a $0.065 per share quarterly cash dividend. The dividend is payable on February 27, 2026 to stockholders of record as of the close of business on February 12, 2026.

Results of Operations and Financial Condition. On January 28, 2026, Tetra Tech, Inc. (“Tetra Tech”) reported its financial results for the first fiscal quarter ended December 28, 2025. A copy of the press release is attached to this report as Exhibit 99.1. Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amen…

CEO — Roger R. Argus: This is an orderly internal succession where the current CEO transitions to Executive Chairman and the President is promoted to CEO, representing a planned leadership change rather than a sudden loss of an executive.

Director — Jeffrey R. Feeler, M. Susan Hardwick: The filing discloses the appointment of two new independent directors to the Board, which is a routine governance event and not a departure of a senior executive.

Results of Operations and Financial Condition. On November 12, 2025, Tetra Tech, Inc. (“Tetra Tech”) reported its financial results for the fourth fiscal quarter ended September 28, 2025. A copy of the press release is attached to this report as Exhibit 99.1. Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as a…

Other Events. On November 12, 2025, Tetra Tech announced that its Board of Directors has declared a $0.065 per share quarterly cash dividend. The dividend is payable on December 12, 2025 to stockholders of record as of the close of business on December 1, 2025.

President — Roger R. Argus: Mr. Argus was promoted to President, overseeing global operations.

Results of Operations and Financial Condition. On July 30, 2025, Tetra Tech, Inc. (“Tetra Tech”) reported its financial results for the third fiscal quarter ended June 29, 2025. A copy of the press release is attached to this report as Exhibit 99.1. Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended.

Other Events. On July 30, 2025, Tetra Tech announced that its Board of Directors has declared a $0.065 per share quarterly cash dividend. The dividend is payable on August 29, 2025 to stockholders of record as of the close of business on August 15, 2025.

Pursuant to the terms of the Credit Agreement, the Company’s ability to pay cash dividends on shares of its common stock will be subject to the Company being in compliance with the financial covenants set forth in the Credit Agreement.

Other Events. On May 7, 2025, the Company announced that its Board of Directors has declared a $0.065 per share quarterly cash dividend. The dividend is payable on June 5, 2025 to stockholders of record as of the close of business on May 23, 2025. 3

Entry into a Material Definitive Agreement. On May 5, 2025, Tetra Tech, Inc. (the “Company”) entered a Fourth Amended and Restated Credit Agreement, among the Company, Tetra Tech Canada Holding Corporation, Tetra Tech UK Holdings Limited, Tetra Tech Australia Group Holdings Pty Ltd, Bank of America, N.A., as administrative agent (the “Administrative Agent”) and the lenders party thereto (the “Credit Agreement”). The Credit Agreement provides for (a) a fully funded $250 million senior secured…

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. The information set forth under

Results of Operations and Financial Condition. On May 7, 2025, the Company reported its financial results for the second fiscal quarter ended March 30, 2025. A copy of the press release is attached to this report as Exhibit 99.1. Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended.

Director — John Douglas: The filing reports the scheduled retirement of a director at the end of his term, which is a routine board succession event rather than a sudden executive departure.

Results of Operations and Financial Condition. On January 29, 2025, Tetra Tech, Inc. (“Tetra Tech”) reported its financial results for the first fiscal quarter ended December 29, 2024. A copy of the press release is attached to this report as Exhibit 99.1. Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amen…

Other Events. On January 29, 2025, Tetra Tech announced that its Board of Directors has declared a $0.058 per share quarterly cash dividend. The dividend is payable on February 26, 2025 to stockholders of record as of the close of business on February 12, 2025.

Other Events. On January 17, 2025, Tetra Tech EC, Inc. (“TtEC”), a wholly owned subsidiary of Tetra Tech, Inc. (the “Company”), entered into a settlement agreement with the United States of America, acting through the Civil Division of the United States Attorney’s Office of the United States Department of Justice and on behalf of the Department of the Navy (collectively, the “United States”), and also filed a proposed consent decree with the United States District Court for the Northern Distr…

Results of Operations and Financial Condition. On November 13, 2024, Tetra Tech, Inc. (“Tetra Tech”) reported its financial results for the fourth fiscal quarter and fiscal year ended September 29, 2024. A copy of the press release is attached to this report as Exhibit 99.1. Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, nor shall it be deemed incorporated by reference in any filing under the Securities A…