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Denison Reports 3.7% EU 3O8 over 3.9 Metres from Initial Follow up Drilling at New High-Grade Basement Uranium Discovery at Waterbury Lake

Exploration Programs

Denison Mines Corp.

1100 – 40 University Ave

Toronto, ON M5J 1T1

www.denisonmines.com

@DenisonMinesCo

PRESS RELEASE

DENISON REPORTS 3.7% eU 3O8 OVER 3.9 METRES FROM INITIAL

FOLLOW UP DRILLING AT NEW HIGH-GRADE BASEMENT URANIUM

DISCOVERY AT WATERBURY LAKE

Toronto, ON – August 22, 2017 Denison Mines Corp. (“Denison” or the “Company”) (DML: TSX, DNN:

NYSE MKT) is pleased to report that drill hole WAT17-446A returned a mineralized interval of 3.7% eU 3O8

over 3.9 metres (from 305.7 to 309.6 metres), inclu ding 7.8% eU 3O8 over 1.8 metres (from 307.0 to 308.8

metres). Drill hole WAT17-446A was the fourth hole completed as part of the summer 2017 drilling program

at the Waterbury Lake property and was drilled approximately 50 metres along strike to the west of WAT17-

443, which intersected 1.1% eU 3O8 over 0.8 metres (see Denison’s Press Release dated August 1 st , 2017).

Today’s news is highlighted by the following:

• Results from drill hole WAT17-446A represent a sig nificant increase in the thickness and grades of

the previous high-grade uranium intersections reported from drill hole WAT17-443;

• High-grade uranium mineralization has now been int ersected 50 metres along strike to the west of

the result previously reported in drill hole WAT17-443;

• The east-west trend targeted by the Waterbury Lake summer drilling program remains open in all

directions and follow-up drilling on an approximate 50 x 50 metre spacing is ongoing; and

• In response to the results returned to date, the n umber of drill holes expected to be completed, as

part of the summer 2017 drilling program, has been increased by 50% to 9 drill holes, from an

original plan of 6 drill holes.

Dale Verran, Denison’s Vice President of Exploratio n, commented, “The results from WAT17-446

represent a very promising intersection at quite an early stage of evaluating this exciting new discovery

at Waterbury Lake. The high-grades, apparent contin uity of mineralization, and the degree of structure

and alteration over drill hole step-outs of 50 metr es or more suggest we are dealing with a very

worthwhile exploration target. With an expanded summer drill program, we are certainly looking forward

to further results from our efforts to continue to explore this untested trend.”

New high-grade basement hosted uranium discovery

The summer 2017 drilling program at Waterbury Lake was designed to test an east-west geological trend,

which shares interpreted similarities with the east-west trend that hosts the J Zone and Roughrider deposits,

which are located approximately one kilometer to th e south. Follow-up drilling to the high-grade

mineralization discovered in WAT17-443, the first h ole of the program, is ongoing and has been designe d

to test the basement-hosted mineralized zone on an approximate 50 x 50 m spacing. The priority of the

follow up drilling is to commence an evaluation of the scale of, and controls on mineralization, which is

currently open in all directions.

The second and third follow-up drill holes of the p rogram also intersected mineralization including 0. 5%

eU 3O8 over 0.6 metres (from 346.0 to 346.6 metres) in dr ill hole WAT17-444, located approximately 65

metres down-dip of drill hole WAT17-443, and 0.2% e U 3O8 over 0.6 metres (from 277.2 to 277.7 metres)

in drill hole WAT17-445, located approximately 60 m etres up-dip of drill hole WAT17-446A. The location s

of the drill hole collars and the J Zone and Roughrider deposits are provided in Figure 1.

Results are reported herein as preliminary radiomet ric equivalent grades ("eU 3O8") derived from a

calibrated downhole total gamma probe. The Company subsequently reports definitive assay grades

following sampling and chemical analysis of the min eralized drill core. The four drill holes completed are

orientated steeply to the southeast with azimuths o f 152°to 157°and dips of -73° to -75.5°. The Athaba sca

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Group sandstones are approximately 200 metres thick, unconformably overlying a moderately north dipping

package of basement rocks dominated by pelitic to s emi-pelitic gneisses. Mineralization in the four ho les

completed has been intersected at depths of 70 to 130 metres vertically below the unconformity in variably

graphitic pelitic gneisses and associated with a wide envelope of strong hematite alteration, quartz flooding,

bleaching and faulting – features typical of baseme nt-hosted uranium mineralization within the Athabas ca

Basin. The true thickness of the mineralization is yet to be determined.

Waterbury summer drilling program to be increased by 50%

As a result of the successful follow-up results fro m drill hole WAT17-446A, which returned a significa nt

increase in the thickness and grades from the initi al results reported from drill hole WAT17-443, Deni son

has decided to increase the scope of the summer 201 7 drilling program at Waterbury Lake from 6 holes

(2,650 metres), as originally planned, to 9 holes (3,850 metres).

Waterbury Lake Property

The Waterbury Lake property consists of multiple cl aims covering 40,256 hectares, and is located in th e

infrastructure rich eastern portion of the Athabasc a Basin region in northern Saskatchewan. The prope rty

is jointly owned by Denison (63.63%) and Korea Wate rbury Uranium Limited Partnership (“KWULP”)

(36.37%) through the Waterbury Lake Uranium Limited Partnership (“WLULP”). KWULP consists of a

consortium of investors in which Korea Hydro & Nuclear Power (“KHNP”) holds a majority position. KWULP

has elected not to fund the 2017 exploration progra m and, as a result, will incur dilution of its owne rship

interest in the WLULP. KHNP is also a significant shareholder in Denison, holding 58,284,000 common

shares of Denison, which represents approximately 1 0.42% of the Company’s issued and outstanding

common shares.

For more information on the J Zone deposit, please refer to the Technical Report on the Mineral Resource

Estimate on the J Zone Uranium Deposit, Waterbury L ake Property dated September 6, 2013 by Allan

Armitage, Ph. D., P. Geo, and Alan Sexton, M.Sc., P .Geo, of GeoVector Management Inc. available on

Denison’s website and under the Company’s profile on SEDAR (www.sedar.com). For further details on

the Roughrider deposit, prior to acquisition by Rio Tinto in 2012, please refer to the Preliminary Eco nomic

Assessment Technical Report for the East and West Z ones Roughrider Uranium Project, Saskatchewan

dated September 2013, 2011 by SRK Consulting (Canada) Inc. available on SEDAR.

Qualified Persons and Data Quality

Dale Verran, MSc, P.Geo, Pr.Sci.Nat., Denison's Vice President, Exploration, who is a Qualified Person in

accordance with the requirements of NI 43-101 has r eviewed and approved the technical information

contained in this release. The Company currently re ports preliminary radiometric equivalent grades

("eU 3O8"), derived from a calibrated downhole total gamma probe, during its exploration programs and

subsequently reports definitive assay grades follow ing sampling and chemical analysis of the mineraliz ed

drill core. Radiometric equivalent probe results ar e subject to verification procedures by qualified p ersons

employed by Denison prior to disclosure. For furthe r details on the total gamma downhole probe methods

employed by Denison, QAQC procedures and data verif ication procedures please see Denison's Annual

Information Form dated March 23, 2017 filed under the Company's profile on SEDAR.

About Denison

Denison is a uranium exploration and development company with interests focused in the Athabasca Basin

region of northern Saskatchewan, Canada. In addition to its 60% owned Wheeler River project, which hosts

the high grade Phoenix and Gryphon uranium deposits , Denison's exploration portfolio consists of

numerous projects covering approximately 359,000 he ctares in the Athabasca Basin region, including

340,000 hectares in the infrastructure rich eastern portion of the Athabasca Basin. Denison's interest s in

Saskatchewan also include a 22.5% ownership interest in the McClean Lake joint venture (“MLJV”), which

includes several uranium deposits and the McClean L ake uranium mill, which is currently processing ore

from the Cigar Lake mine under a toll milling agreement, plus a 25.17% interest in the Midwest deposit and

a 63.63% interest in the J Zone deposit on the Wate rbury Lake property. Both the Midwest and J Zone

deposits are located within 20 kilometres of the McClean Lake mill.

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Denison is also engaged in mine decommissioning and environmental services through its Denison

Environmental Services division and is the manager of Uranium Participation Corp., a publicly traded

company which invests in uranium oxide and uranium hexafluoride.

For more information, please contact

David Cates (416) 979-1991 ext. 362

President and Chief Executive Officer

Sophia Shane (604) 689-7842

Investor Relations

Follow Denison on Twitter @DenisonMinesCo

Cautionary Statement Regarding Forward-Looking Statements

Certain information contained in this press release constitutes "forward-looking information", within the meaning of the United States

Private Securities Litigation Reform Act of 1995 an d similar Canadian legislation concerning the busin ess, operations and financial

performance and condition of Denison.

Generally, these forward-looking statements can be identified by the use of forward-looking terminolog y such as "plans", "expects",

"budget", "scheduled", "estimates", "forecasts", "intends", "anticipates", or "believes", or the negatives and/or variations of such words and

phrases, or state that certain actions, events or results "may", "could", "would", "might" or "will be taken", "occur", "be achieved" or "has

the potential to". In particular, this press release contains forward-looking information pertaining to the following: exploration (including

drilling) and evaluation activities, plans and objectives, and Denison’s percentage in its properties and its plans and agreements with its

joint venture partners, as applicable. Statements relating to "mineral reserves" or "mineral resources" are deemed to be forward-looking

information, as they involve the implied assessment, based on certain estimates and assumptions that the mineral reserves and mineral

resources described can be profitably produced in the future.

Forward looking statements are based on the opinions and estimates of management as of the date such statements are made, and they

are subject to known and unknown risks, uncertainties and other factors that may cause the actual results, level of activity, performance

or achievements of Denison to be materially different from those expressed or implied by forward-looking statements. Denison believes

that the expectations reflected in this forward-looking information are reasonable but no assurance can be given that these expectations

will prove to be accurate and may differ materially from those anticipated in this forward looking information. For a discussion in respect

of risks and other factors that could influence forward-looking events, please refer to the factors discussed in Denison's Annual Information

Form dated March 23, 2017 under the heading "Risk Factors". These factors are not, and should not be construed as being exhaustive.

Accordingly, readers should not place undue reliance on forward-looking statements.

The forward-looking information contained in this press release is expressly qualified by this cautionary statement. Any forward-looking

information and the assumptions made with respect thereto speaks only as of the date of this press release. Denison does not undertake

any obligation to publicly update or revise any forward-looking information after the date of this press release to conform such information

to actual results or to changes in Denison's expectations except as otherwise required by applicable legislation .

Cautionary Note to United States Investors Concerning Estimates of Measured, Indicated and Inferred Mineral Resources: This

press release may use the terms “measured”, “indicated” and “inferred” mineral resources. United States investors are advised that while

such terms are recognized and required by Canadian regulations, the United States Securities and Exchange Commission does not

recognize them. “Inferred mineral resources” have a great amount of uncertainty as to their existence, and as to their economic and legal

feasibility. It cannot be assumed that all or any part of an inferred mineral resource will ever be upgraded to a higher category. Under

Canadian rules, estimates of inferred mineral resources may not form the basis of feasibility or other economic studies. United States

investors are cautioned not to assume that all or any part of measured or indicated mineral resources will ever be converted into mineral

reserves. United States investors are also cautioned not to assume that all or any part of an inferred mineral resource exists, or is

economically or legally mineable.

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Figure 1: Location of summer 2017 drill collars on Denison’s Waterbury Lake project.