Exhibit 99.1

NEWS RELEASE  July 29, 2026

Tetra Tech Reports Strong Third Quarter 2026 Results

Pasadena, California. Tetra Tech, Inc. (NASDAQ: TTEK), a global provider of high-end technical and engineering services, Leading with Science^® in water, environment and sustainable infrastructure, today announced results for the third quarter ended June 28, 2026.

Revenue and revenue, net of subcontractor costs (net revenue)¹, in the third quarter totaled $1.31 billion and $1.11 billion, respectively. Net revenue increased 8% Y/Y excluding USAID / DOS and episodic disaster response. Operating income was $158 million, EBITDA¹ was $173 million, and EPS was $0.42. Backlog was $4.49 billion at the end of the third quarter, up 5% sequentially. Cash from operations was $229 million in the third quarter and $567 million over the trailing twelve months, resulting in a DSO of 56 days.

Recent Key Wins

Executive Management Comments

Roger Argus, Chief Executive Officer, commented, “We delivered a strong third quarter with growth primarily driven by U.S. federal and international end markets, both increasing at a double-digit rate. We received significant new orders during the quarter, including commercial orders for data center and sediment restoration projects, driving our backlog up by more than $200 million. The Company’s performance year-to-date resulted in our increasing guidance for fiscal 2026.”

Steve Burdick, Chief Financial Officer, stated, “Tetra Tech generated its strongest cash flow on record with $467 million from operations through the first three quarters of fiscal 2026. Our ability to consistently generate more cash than net income has allowed the Company to fund acquisitions, increase the stock buybacks, and pay higher dividends, while still deleveraging our net debt.”

Quarterly Dividend and Share Repurchase Program

On July 27, 2026, Tetra Tech’s Board of Directors approved a quarterly dividend in the amount of $0.072 per share, an 11% increase year-over-year, payable on August 27, 2026, to stockholders of record as of August 13, 2026. This is the 45^th consecutive double-digit increase in the Company’s quarterly dividend. In the third quarter of fiscal 2026, Tetra Tech repurchased $100 million of common stock. Additionally, as of June 28, 2026, the Company had $398 million remaining under its share repurchase program.

Nine-Month Results

Revenue for the nine-month period was $3.74 billion and net revenue was $3.20 billion. Net revenue increased 8% Y/Y excluding USAID / DOS and episodic disaster response. Operating income was $430 million, adjusted EBITDA was $466 million, and EPS was $1.18; cash flows generated from operations were $467 million.

Business Outlook

The following statements are based on current expectations. These statements are forward-looking, and the actual results could differ materially. These statements do not include the potential impact of transactions that may be completed or developments that become evident after the date of this release. The Business Outlook section should be read in conjunction with the information on forward-looking statements at the end of this release.

For the fourth quarter of fiscal 2026, Tetra Tech expects net revenue² to range from $1.12 billion to $1.17 billion and EPS to range from $0.45 to $0.48. For fiscal 2026, Tetra Tech is increasing adjusted EPS³ guidance to range from $1.56 to $1.59. Tetra Tech is narrowing the fiscal 2026 net revenue range to $4.315 billion to $4.365 billion, which represents an increased midpoint for the year.

Webcast

Investors will have the opportunity to access a live audio-visual webcast and supplemental financial information concerning the third quarter of fiscal 2026 results through a link posted on the Company’s website at tetratech.com on July 30, 2026, at 8:00 a.m. (PT).

About Tetra Tech

Tetra Tech is the leader in water, environment and sustainable infrastructure, providing high-end technical and engineering services for projects worldwide. With more than 25,000 employees working together, Tetra Tech provides clear solutions to complex problems by Leading with Science^® to address the entire water cycle, protect and restore the environment, and design sustainable and resilient infrastructure. For more information about Tetra Tech, please visit tetratech.com or follow us on LinkedIn and Facebook.

CONTACTS:
Jim Wu, Investor Relations
Charlie MacPherson, Media & Public Relations
(626) 470-2844

Forward-Looking Statements

This release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. The use of words such as "anticipate," "expect," "could," "may," "intend," "plan" and "believe," among others, generally identify forward-looking statements. These forward-looking statements are based on current expectations and beliefs of Tetra Tech’s management and currently available operating, financial, economic and other information, and are subject to a number of risks and uncertainties. Readers are cautioned that these forward-looking statements are only predictions and may differ materially from actual future events or results. A variety of factors, many of which are beyond our control, could cause actual future results or events to differ materially from those projected in the forward-looking statements in this release, including but not limited to: continuing worldwide political and economic uncertainties; the U.S. Administration’s potential changes to fiscal policies; the cyclicality in demand for our overall services; the fluctuation in demand for oil and gas, and mining services; risks related to international operations; concentration of revenues from U.S. government agencies and potential funding disruptions by these agencies; dependence on winning or renewing U.S. government contracts; the delay or unavailability of public funding on U.S. government contracts; the U.S. government’s right to modify, delay, curtail or terminate contracts at its convenience; compliance with government procurement laws and regulations; the impact of global pandemics; credit risks associated with certain clients in certain geographic areas or industries; acquisition strategy and integration risks; goodwill or other intangible asset impairment; the failure to comply with worldwide anti-bribery laws; the failure to comply with domestic and international export laws; the failure to properly manage projects; the loss of key personnel or the inability to attract and retain qualified personnel; the ability of our employees to obtain government granted eligibility; the use of estimates and assumptions in the preparation of financial statements; the ability to maintain adequate workforce utilization; the use of the percentage-of-completion method of accounting; the inability to accurately estimate and control contract costs; the failure to adequately recover on our claims for additional contract costs; the failure to win or renew contracts with private and public sector clients; growth strategy management; backlog cancellation and adjustments; risks relating to cyber security breaches; the failure of partners to perform on joint projects; the failure of subcontractors to satisfy their obligations; requirements to pay liquidated damages based on contract performance; the adoption of new legal requirements; changes in resource management, environmental or infrastructure industry laws, regulations or programs; changes in bank and capital markets and the access to capital; credit agreement covenants; industry competition; liability related to legal proceedings, investigations, and disputes; the availability of third-party insurance coverage; the ability to obtain adequate bonding; employee, agent, or partner misconduct; employee risks related to international travel; safety programs; conflict of interest issues; liabilities relating to reports and opinions; liabilities relating to environmental laws and regulations; force majeure events; protection of intellectual property rights; stock price volatility; the ability to impede a business combination based on Delaware law and charter documents; and other risks and uncertainties as may be described in Tetra Tech’s periodic filings with the Securities and Exchange Commission, including those described in the “Risk Factors” section of Tetra Tech’s Annual Report on Form 10-K for the fiscal year ended September 28, 2025. Readers should not place undue reliance on forward-looking statements since such information speaks only as of the date of this release. Tetra Tech does not intend to update forward-looking statements and expressly disclaims any obligation to do so.

Non-GAAP Financial Measures

To supplement the financial results presented in accordance with generally accepted accounting principles in the United States (“GAAP”), we present certain non-GAAP financial measures within the meaning of Regulation G under the Securities Exchange Act of 1934, as amended. We provide these non-GAAP financial measures because we believe they provide a valuable perspective on our financial results. However, non-GAAP measures have limitations as analytical tools and should not be considered in isolation and are not in accordance with, or a substitute for, GAAP measures. In addition, other companies may define non-GAAP measures differently which limits the ability of investors to compare non-GAAP measures of Tetra Tech to those used by our peer companies. A reconciliation of these non-GAAP financial measures to the most directly comparable GAAP financial measures is set forth in this release.

Tetra Tech, Inc.

Balance Sheet - Unaudited

(unaudited - in thousands, except par value)

Tetra Tech, Inc.

Regulation G Information

June 28, 2026

Reconciliation of Revenue to Revenue, Net of Subcontractor Costs (“Net Revenue”)

(in millions)

Reconciliation of Net Income Attributable to Tetra Tech to Adjusted EBITDA

(in thousands)

¹ Includes write-off of deferred debt origination fees of $3.8M in fiscal 2023

² Includes lease impairment charge of $16.4M in fiscal 2023