Exhibit 99.1

July 21, 2004

Tetra Tech Reports Third Quarter 2004 Results

Pasadena, California. Tetra Tech, Inc. (NASDAQ: TTEK) today announced third quarter results for fiscal year 2004. Revenue for the quarter ended June 27, 2004 was $375.5 million, up 19.8% from revenue of $313.6 million for the same quarter last year. Revenue, net of subcontractor costs, for the quarter was $263.2 million, up 13.5% from $231.8 million a year ago. Income from operations for the quarter was $17.4 million, 31.8% less than the $25.6 million for last year’s third quarter. Net income for the quarter was $9.0 million, down 34.6% from $13.8 million a year ago. Diluted earnings per share were 16 cents compared to 25 cents for the previous year, a 36.0% decrease.

Revenue for the nine months ended June 27, 2004 was $1,044.0 million, up 31.8% from revenue of $792.1 million for the same period last year. Revenue, net of subcontractor costs, for the nine months was $747.7 million, up 23.5% from $605.6 million a year ago. Income from operations for the nine-month period was $65.3 million, 2.1% more than the $64.0 million for the nine-month period last year. Net income for the nine-month period was $35.0 million, compared to a net loss of $80.3 million last year due to cumulative effect of an accounting change of $114.7 million in 2003. Diluted earnings per share before the cumulative effect of accounting change for the nine-month period was 61 cents compared to 62 cents last year, a 1.6% decrease.

Summary of Financial Results:

(in thousands, except per share data)

	Third Quarter Ended				Nine Months Ended
	June 27, 2004		June 29, 2003		June 27, 2004		June 29, 2003
Revenue	$	375,527	$	313,556	$	1,044,024	$	792,100
Revenue, Net of Subcontractor Costs	263,174		231,792		747,697		605,644
Income from Operations	17,439		25,564		65,345		64,011
Income Before Cumulative Effect of Accounting Change	9,031		13,811		35,002		34,375
Net Income/(Loss)	9,031		13,811		35,002		(80,294		)

EPS Before Cumulative Effect of Accounting Change:
Basic(1)	0.16		0.25		0.63		0.63
Diluted	0.16		0.25		0.61		0.62
Basic Shares Outstanding(1)	56,104		54,788		55,831		54,639
Diluted Shares Outstanding	57,157		56,086		57,339		55,503

(1) EPS-basic and basic shares outstanding have been revised for the periods ended June 29, 2003 to include 1,235,000 shares of common stock issuable upon the exchange of exchangeable shares of a subsidiary.

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 material corporate transactions that may be completed 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.

Revenue, net of subcontractor costs, for the fourth quarter is expected to range from approximately $260 million to $285 million. Tetra Tech expects diluted earnings per share for the fourth quarter to be approximately 24 cents. However, the Company continues to assess and make changes in its civil infrastructure and communications businesses. The speed of implementing these changes and the stability of market conditions in these business areas will impact the Company’s ability to meet its guidance.

About Tetra Tech (www.tetratech.com)

Tetra Tech is a leading provider of consulting, engineering and technical services. With nearly 9,000 associates located in the United States and internationally, the Company supports commercial and government clients in the areas of resource management and infrastructure. Tetra Tech’s services include research and development, applied science and technology, engineering design, construction management, and operations and maintenance.

Investors will have the opportunity to access a live audio-visual webcast concerning the third quarter results through a link posted on the Company’s website at www.tetratech.com on July 22, 2004 at 8:00 a.m. (PDT)

CONTACT: Li-San Hwang, CEO or Mike Bieber, Investor Relations (626) 351-4664

This news release contains forward-looking statements that are subject to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. These forward-looking statements include information concerning future events and the future financial performance of Tetra Tech that involve risks and uncertainties. Readers are cautioned that these forward-looking statements are only predictions and may differ materially from actual future events or results. Readers are urged to read the documents filed by Tetra Tech with the SEC, specifically the most recent reports on Form 10-K, 10-Q and 8-K, each as it may be amended from time to time, which identify risk factors that could cause actual results to differ materially from the forward-looking statements. Among the important factors or risks that could cause actual results or events to differ materially from those in the forward-looking statements in this release are: acquisition strategy risks; fluctuations in quarterly operating results and stock price; the impact of downturns in the financial markets on clients; management of growth strategy; credit risks associated with commercial clients; the consolidation of client base; loss of key personnel or the inability to attract and retain qualified personnel; changes in existing laws and regulations; concentration of revenues from agencies of the Federal government and reductions in spending by these agencies; audit of contracts with governmental agencies; losses under fixed-price contracts or termination of contracts at the client’s discretion; backlog cancellation or adjustment; inability to find qualified subcontractors; competition; risks of professional and other liabilities; conflict of interest issues; and foreign currency fluctuations. The financial information contained in this release should be read in conjunction with the consolidated financial statements and notes thereto included in Tetra Tech’s most recent reports on Form 10-Q and Form 10-K, each as it may be amended from time to time. Tetra Tech’s results of operations for the fiscal quarter ended June 27, 2004 are not necessarily indicative of Tetra Tech’s operating results for any future periods. Any projections in this release are based on limited information currently available to Tetra Tech, which is subject to change. Although any such projections and the factors influencing them will likely change, Tetra Tech will not necessarily update the information, since Tetra Tech will only provide guidance at certain points during the year. Such information speaks only as of the date of this release.


	TETRA TECH, INC.

Unaudited Investors Report	2000			2001			2002			2003																					2004
($ in Thousands, Except Per Share Data)	Total			Total			Total			1st Qtr			2nd Qtr			6 mos			3rd Qtr			9 mos			4 Qtr			Total			1st Qtr			2nd Qtr			6 mos			3rd Qtr			9 mos
REVENUE	794,578			973,944			966,223			233,080			245,464			478,544			313,556			792,100			339,950			1,132,050			337,102			331,395			668,497			375,527			1,044,024
REVENUE, NET OF SUBCONTRACTOR COST	598,121			730,064			740,715			180,982			192,870			373,852			231,792			605,644			255,128			860,772			241,705			242,818			484,523			263,174			747,697
Resource Management	246,851			292,299			356,983			91,548			105,282			196,830			144,550			341,380			155,556			496,936			142,689			141,661			284,350			147,730			432,080
Infrastructure	343,629			432,642			377,888			87,800			86,029			173,829			86,536			260,365			96,640			357,005			97,179			99,173			196,352			113,339			309,691
Elimination/Other	7,641			5,123			5,844			1,634			1,559			3,193			706			3,899			2,932			6,831			1,837			1,984			3,821			2,105			5,926
GROSS PROFIT	145,249			170,590			158,562			37,608			41,795			79,403			49,871			129,274			51,340			180,614			47,859			48,117			95,976			43,423			139,399
GROSS PROFIT %	24.3		%	23.4		%	21.4		%	20.8		%	21.7		%	21.2		%	21.5		%	21.3		%	20.1		%	21.0		%	19.8		%	19.8		%	19.8		%	16.5		%	18.6		%
SEGMENT INCOME FROM OPERATIONS	80,708			58,434			71,233			17,258			21,505			38,763			25,971			64,734			29,704			94,438			24,467			24,526			48,993			18,144			67,137
Resource Management	32,901			35,034			44,902			10,141			10,333			20,474			17,841			38,315			21,329			59,644			14,392			18,429			32,821			16,649			49,470
Infrastructure	48,886			23,120			31,377			7,166			9,796			16,962			8,536			25,498			5,299			30,797			9,764			6,985			16,749			1,810			18,559
Elimination/Other	(1,079		)	280			(5,046		)	(49		)	1,376			1,327			(406		)	921			3,076			3,997			311			(888		)	(577		)	(315		)	(892		)
SEGMENT INCOME FROM OPERATIONS %	13.5		%	8.0		%	9.6		%	9.5		%	11.1		%	10.4		%	11.2		%	10.7		%	11.6		%	11.0		%	10.1		%	10.1		%	10.1		%	6.9		%	9.0		%
Resource Management	13.3		%	12.0		%	12.6		%	11.1		%	9.8		%	10.4		%	12.3		%	11.2		%	13.7		%	12.0		%	10.0		%	12.8		%	11.4		%	11.1		%	11.3		%
Infrastructure	14.2		%	5.3		%	8.3		%	8.2		%	11.4		%	9.8		%	9.9		%	9.8		%	5.5		%	8.6		%	10.0		%	7.0		%	8.5		%	1.6		%	6.0		%
Amortization Expense	6,463			9,192			10,811			135			181			316			407			723			563			1,286			526			561			1,087			705			1,792
INCOME FROM OPERATIONS	74,245			49,242			60,422			17,123			21,324			38,447			25,564			64,011			29,141			93,152			23,941			23,965			47,906			17,439			65,345
Net Interest Expense	7,026			8,543			5,453			1,892			2,281			4,173			2,546			6,719			2,555			9,274			2,372			2,249			4,621			2,387			7,008
PRE-TAX INCOME	67,219			40,699			54,969			15,231			19,043			34,274			23,018			57,292			26,586			83,878			21,569			21,716			43,285			15,052			58,337
Income Tax Expense	26,777			9,874			23,059			6,092			7,618			13,710			9,207			22,917			10,852			33,769			8,627			8,687			17,314			6,021			23,335
Effective Tax Rate	39.8		%	24.3		%	41.9		%	40.0		%	40.0		%	40.0		%	40.0		%	40.0		%	40.8		%	40.3		%	40.0		%	40.0		%	40.0		%	40.0		%	40.0		%
NET INCOME	40,442			30,825			31,910			(105,530		)	11,425			(94,105		)	13,811			(80,294		)	15,734			(64,560		)	12,942			13,029			25,971			9,031			35,002
DILUTED AVERAGE SHARES	52,003			54,166			55,086			55,005			55,419			55,212			56,086			55,503			56,616			55,782			57,395			57,465			57,430			57,157			57,339
DILUTED EPS, AS REPORTED	$	0.78		$	0.57		$	0.58		$	0.17		$	0.21		$	0.37		$	0.25		$	0.62		$	0.28		$	0.90		$	0.23		$	0.23		$	0.45		$	0.16		$	0.61
SPECIAL ITEMS
Pre-Acquisition Reserve Reversal	2,000			—			—			—			—			—			—			—			—			—			—			—			—			—			—
Tax Credits	1,456			7,028			—			—			—			—			—			—			—			—			—			—			—			—			—
Bankruptcy Reserves	—			(38,300		)	—			—			—			—			—			—			—			—			—			—			—			—			—
Judgment Reserve	—			—			(4,100		)	—			—			—			—			—			—			—			—			—			—			—			—
Cumulative Effect of Accounting Change (142)	—			—			—			(114,669		)	—			(114,669		)	—			(114,669		)	—			(114,669		)	—			—			—			—			—
Net Income Impact	2,616			(16,335		)	(2,468		)	(114,669		)	—			(114,669		)	—			(114,669		)	—			(114,669		)	—			—			—			—			—
DILUTED EPS, BEFORE U/I ITEMS	$	0.73		$	0.87		$	0.62		$	0.17		$	0.21		$	0.37		$	0.25		$	0.62		$	0.28		$	0.90		$	0.23		$	0.23		$	0.45		$	0.16		$	0.61
EBITDA
EBIT Before Unusual or Infrequent	74,245			49,242			60,422			(97,546		)	21,324			(76,222		)	25,564			(50,658		)	29,141			(21,517		)	23,941			23,965			47,906			17,439			65,345
Depreciation	7,246			12,170			12,543			3,180			3,286			6,466			4,240			10,706			4,378			15,084			3,815			3,693			7,508			3,889			11,397
Amortization	6,463			9,192			10,811			135			181			316			407			723			563			1,286			526			561			1,087			705			1,792
EBITDA, AS REPORTED	87,954			70,604			83,776			(94,231		)	24,791			(69,440		)	30,211			(39,229		)	34,082			(5,147		)	28,282			28,219			56,501			22,033			78,534
DAYS SALES RECEIVABLES	97.3			93.9						94.8			93.3						91.1						84.9						92.6			90.7						94.1			—
Resource Management	75.3			79.6						78.2			78.0						70.9						65.1						70.6			68.8						72.2			—
Infrastructure	112.8			106.1						113.8			119.3						125.0						119.5						130.6			116.6						121.3			—
CASH FLOW FROM OPERATIONS	(12,188		)	44,274			95,211			(2,035		)	(7,398		)	(9,433		)	33,617			24,184			42,582			66,766			(23,322		)	13,122			(10,200		)	(12,113		)	(22,313		)
CAPITAL EXPENDITURES	14,745			11,017			7,231			1,705			2,295			4,000			2,657			6,657			3,162			9,819			4,319			2,893			7,212			3,873			11,085
Y/Y NET REVENUE GROWTH %	38.4		%	22.5		%	1.5		%	-2.1		%	8.3		%	3.0		%	25.0		%	10.4		%	32.7		%	16.2		%	33.6		%	25.9		%	29.6		%	13.5		%	23.5		%
Resource Management	6.6		%	19.4		%	22.1		%	9.1		%	21.7		%	15.5		%	62.7		%	31.7		%	59.2		%	39.2		%	55.1		%	34.4		%	44.1		%	3.2		%	26.9		%
Infrastructure	71.4		%	25.9		%	-12.7		%	-11.8		%	-4.6		%	-8.4		%	-9.1		%	-8.6		%	3.9		%	-5.5		%	10.7		%	15.3		%	13.0		%	31.0		%	18.9		%
Y/Y NET REVENUE ORGANIC GROWTH %	12.0		%	8.4		%	-10.1		%	-13.0		%	-6.3		%	-9.7		%	-2.7		%	-7.3		%	4.4		%	-4.3		%	1.9		%	0.5		%	1.2		%	2.6		%	1.8		%
NET REVENUE % BY CLIENT TYPE
Federal Government	29.1		%	24.5		%	25.1		%	24.1		%	27.8		%	26.0		%	38.4		%	30.7		%	39.5		%	33.3		%	41.0		%	42.0		%	41.5		%	43.8		%	42.3		%
State & Local Government	16.3		%	18.1		%	23.5		%	23.4		%	23.4		%	23.4		%	20.0		%	22.1		%	16.6		%	20.5		%	17.1		%	16.2		%	16.7		%	15.7		%	16.3		%
Private Sector	51.4		%	54.2		%	49.1		%	50.4		%	47.0		%	48.6		%	40.3		%	45.5		%	42.3		%	44.5		%	40.2		%	39.0		%	39.6		%	37.5		%	38.9		%
International	3.2		%	3.2		%	2.3		%	2.1		%	1.8		%	2.0		%	1.4		%	1.7		%	1.6		%	1.7		%	1.7		%	2.8		%	2.2		%	3.0		%	2.5		%
AVERAGE FULL-TIME EQUIVALENTS	5,529			6,512			6,775			6,866			6,982			6,924			7,776			7,208			8,000			7,406			8,057			7,964			8,010			8,136			8,052
BACKLOG	632,859			634,706			715,834			715,742			998,762			998,762			1,004,671			1,004,671			1,045,400			1,045,400			1,000,544			1,049,154			1,049,154			1,152,659			1,152,659

TETRA TECH, INC.

Unaudited Statements of Operations

(unaudited - in thousands, except per share data)

	Three Months Ended							Nine Months Ended
	June 27, 2004			June 29, 2003			% Change	June 27, 2004			June 29, 2003			% Change
Revenue	$	375,527		$	313,556		19.8	$	1,044,024		$	792,100		31.8
Subcontractor costs	112,353			81,764			37.4	296,327			186,456			58.9
Revenue, net of subcontractor costs	263,174			231,792			13.5	747,697			605,644			23.5
Other contract costs	219,751			181,921			20.8	608,298			476,370			27.7
Gross profit	43,423			49,871			-12.9	139,399			129,274			7.8
Selling, general and administrative expenses	25,984			24,307			6.9	74,054			65,263			13.5
Income from operations	17,439			25,564			-31.8	65,345			64,011			2.1
Interest expense - net	2,387			2,546			-6.2	7,008			6,719			4.3
Income before income tax expense	15,052			23,018			-34.6	58,337			57,292			1.8
Income tax expense	6,021			9,207			-34.6	23,335			22,917			1.8
Income before cumulative effect of accounting change	9,031			13,811			-34.6	35,002			34,375			1.8
Cumulative effect of accounting change	—			—			—	—			(114,669		)	-100.0
Net income (loss)	$	9,031		$	13,811		-34.6	$	35,002		$	(80,294	)	-143.6
Earnings per share before cumulative effect of accounting change - diluted	$	0.16		$	0.25		-36.0	$	0.61		$	0.62		-1.6
Weighted average shares outstanding - diluted	57,157			56,086			1.9	57,339			55,503			3.3
Percentage of revenue, net of subcontractor costs
Revenue, net of subcontractor costs	100.0		%	100.0		%		100.0		%	100.0		%
Other contract costs	83.5		%	78.5		%		81.4		%	78.7		%
Gross profit	16.5		%	21.5		%		18.6		%	21.3		%
Selling, general and administrative expenses	9.9		%	10.5		%		9.9		%	10.8		%
Income from operations	6.6		%	11.0		%		8.7		%	10.5		%
Interest expense - net	0.9		%	1.1		%		0.9		%	1.1		%
Income before income tax expense	5.7		%	9.9		%		7.8		%	9.4		%
Income tax expense	2.3		%	4.0		%		3.1		%	3.8		%
Income before cumulative effect of accounting change	3.4		%	5.9		%		4.7		%	5.6		%
Cumulative effect of accounting change	—			—				—			-18.9		%
Net income (loss)	3.4		%	5.9		%		4.7		%	-13.3		%

TETRA TECH, INC.

Condensed Consolidated Balance Sheets

(in thousands, except par value)

	June 27, 2004			September 28, 2003
	(Unaudited)
ASSETS
CURRENT ASSETS:
Cash and cash equivalents	$	38,900		$	33,164
Accounts receivable - net	209,047			167,717
Unbilled receivables - net	193,512			164,818
Contract retentions	5,463			4,286
Prepaid expenses and other current assets	28,999			26,037
Income taxes receivable	34,834			20,825
Total current assets	510,755			416,847

PROPERTY AND EQUIPMENT:
Equipment, furniture and fixtures	84,817			84,133
Leasehold improvements	10,535			10,123
Total	95,352			94,256
Accumulated depreciation and amortization	(56,444		)	(53,469		)
PROPERTY AND EQUIPMENT - NET	38,908			40,787

GOODWILL	253,045			210,792

INTANGIBLE AND OTHER ASSETS - NET	27,799			25,054

TOTAL ASSETS	$	830,507		$	693,480

LIABILITIES AND STOCKHOLDERS’ EQUITY
CURRENT LIABILITIES:
Accounts payable	$	105,010		$	93,265
Accrued compensation	54,097			46,743
Billings in excess of costs on uncompleted contracts	20,288			16,307
Other current liabilities	32,395			26,562
Deferred income taxes	28,728			28,992
Current portion of long-term obligations	88,128			11,597
Total current liabilities	328,646			223,466

LONG - TERM OBLIGATIONS	91,182			107,463

COMMITMENTS AND CONTINGENCIES

STOCKHOLDERS’ EQUITY:
Preferred stock - authorized, 2,000 shares of $0.01 par value; no shares issued and outstanding at June 27, 2004 and September 28, 2003	—			—
Exchangeable stock of a subsidiary	13,228			13,239
Common stock - authorized, 85,000 shares of $0.01 par value; issued and outstanding 56,185 and 54,090 shares at June 27, 2004 and September 28, 2003, respectively	562			541
Additional paid-in capital	230,238			216,908
Accumulated other comprehensive loss	(601		)	(387		)
Retained earnings	167,252			132,250
TOTAL STOCKHOLDERS’ EQUITY	410,679			362,551

TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$	830,507		$	693,480

TETRA TECH, INC.

Condensed Consolidated Statements of Cash Flows

(unaudited - in thousands)

	Three Months Ended						Nine Months Ended
	June 27, 2004			June 29, 2003			June 27, 2004			June 29, 2003
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$	9,031		$	13,811		$	35,002		$	(80,294	)

Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Cumulative effect of accounting change	—			—			—			114,669
Depreciation and amortization	4,708			4,646			13,531			11,429
Deferred income taxes	(377		)	—			(264		)	—
Provision for losses on receivables	4,505			1,368			6,840			3,221
Loss on disposal of property and equipment	25			170			729			170

Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	(35,290		)	(8,170		)	(44,498		)	(3,228		)
Unbilled receivables	(12,432		)	6,768			(29,382		)	(6,002		)
Contract retentions	(706		)	1,113			(1,177		)	1,442
Prepaid expenses and other assets	(6,948		)	(1,490		)	(6,166		)	(4,223		)
Accounts payable	12,468			4,145			2,211			(16,877		)
Accrued compensation	10,104			8,061			6,084			5,458
Billings in excess of costs on uncompleted contracts	2,344			(2,136		)	3,981			(1,608		)
Other current liabilities	3,935			(2,424		)	2,427			322
Income taxes receivable	(3,480		)	7,755			(11,631		)	(295		)
Net cash (used in) provided by operating activities	(12,113		)	33,617			(22,313		)	24,184

CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(3,873		)	(2,657		)	(11,085		)	(6,657		)
Payments for business acquisitions, net of cash acquired	—			121			(31,371		)	(72,072		)
Proceeds on sale of property and equipment	81			1,086			982			1,086
Net cash used in investing activities	(3,792		)	(1,450		)	(41,474		)	(77,643		)

CASH FLOWS FROM FINANCING ACTIVITIES:
Payments on long-term obligations	(21,974		)	(32,613		)	(65,074		)	(38,188		)
Proceeds from borrowings under long-term obligations	38,000			4,500			125,324			69,500
Net proceeds from issuance of common stock	4,405			4,380			9,468			5,055
Net cash provided by (used in) financing activities	20,431			(23,733		)	69,718			36,367

EFFECT OF EXCHANGE RATE CHANGES ON CASH	(282		)	(256		)	(195		)	336

NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	4,244			8,178			5,736			(16,756		)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	34,656			21,411			33,164			46,345

CASH AND CASH EQUIVALENTS AT END OF PERIOD	$	38,900		$	29,589		$	38,900		$	29,589

SUPPLEMENTAL CASH FLOW INFORMATION:
Cash paid during the period for:
Interest	$	4,426		$	5,189		$	9,244		$	9,508
Income taxes, net of refunds received	$	9,874		$	678		$	34,866		$	22,818