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Denison Receives Provincial Environmental Assessment Approval for the Wheeler River Project

Permits & Approvals

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Denison Mines Corp.

1100 – 40 University Ave

Toronto, ON M5J 1T1

www.denisonmines.com

PRESS RELEASE

Denison Receives Provincial Environmental Assessment Approval

for the Wheeler River Project

Toronto, ON – August 5, 2025. Denison Mines Corp. (“Denison” or the “Company”) (TSX: DML; NYSE

American: DNN) is pleased to announce that it has received Ministerial approval under The Environmental

Assessment Act (Saskatchewan) to proceed with the development of the In-Situ Recovery (“ISR”) uranium

mine planned for the Wheeler River Project (the “Project”).

As part of Denison’s strategy to effectively harmonize the Federal and Provincial Environmental

Assessment (the “EA”) for the Project, the Provincial EA was submitted for final approval in late 2024 after

Denison successfully completed multiple key milestones in the Federal regulatory process, including

completion of the Canadian Nuclear Safety Commission’s (“CNSC”) rigorous technical review phase, and

acceptance by the CNSC of the Company's final Environmental Impact Statement (“EIS”) for the Project.

As a result of this approach, the Federal and Provincial EAs for the Project are substantially the same and

no subsequent revisions for conformance are expected to be required.

“Saskatchewan is the world’s second-largest uranium producer, and remains a destination of

choice for mining investment due to our abundant natural resources and strong regulatory

environment,” Saskatchewan Premier Scott Moe said. “The province continues to be a national leader

in safe and sustainable mining practices, well positioning Canada as an emerging energy

superpower. As demand for these resources increase, we are pleased to see this project move

ahead, further enhancing Saskatchewan’s world class energy sector, while bringing new jobs and

opportunities to northern communities.”

“I would like to congratulate Denison Mines on this significant project milestone with their Wheeler

River Project”, commented the Honourable Travis Keisig, Saskatchewan Minister of Environment. “We

look forward to working with Denison as this project progresses and are excited that they have

chosen Saskatchewan as a place to do business.”

David Cates, President and CEO of Denison, commented, “We thank the Province of Saskatchewan for

entrusting Denison to proceed with the development of the Project, which is expected to set a

superior standard of sustainability as the first ISR uranium mine in Canada. We applaud the work

of the Provincial Government to uphold the province’s rigorous environmental regulations, while

simultaneously recognizing the important role that the natural resources sector can play in driving

societal wellbeing. The Province of Saskatchewan is truly a leading jurisdiction for sustainable

natural resource investments.

I’d also like to applaud our own environmental, regulatory, sustainability and technical teams for

working closely with the Saskatchewan Ministry of the Environment, Indigenous nations, local

communities, and other interested parties during the EA process. Importantly, completion of the

provincial EA represents one of the final regulatory milestones necessary for Denison to commence

construction of the Phoenix ISR mine, which is on track to become Canada’s next new large-scale

uranium mine.”

With the Provincial EA approved, the remaining regulatory requirements to commence construction of the

ISR mine planned for the Phoenix deposit include receipt of the Provincial Pollutant Control Facility Permit,

as well as the Federal approval of the EA and receipt of the Federal License to Prepare the Site & Construct.

Both outstanding Federal approvals are the subject of the CNSC public hearings for the Project scheduled

in October and December 2025.

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About Wheeler River

Wheeler River is the largest undeveloped uranium project in the infrastructure -rich eastern portion of the

Athabasca Basin region, in northern Saskatchewan. The project is host to the high- grade Phoenix and

Gryphon uranium deposits, discovered by Denison in 2008 and 2014, respectively, and is a joint venture

between Denison (90% and operator) and JCU (Canada) Exploration Company Limited ( “JCU”, 10%). In

August 2023, Denison filed a technical report summarizing the results of (i) the feasibility study completed

for ISR mining of the high-grade Phoenix uranium deposit and (ii) a cost update to the 2018 Pre-Feasibility

Study for conventional underground mining of the basement -hosted Gryphon uranium deposit. More

information on the studies is available in the technical report titled “ NI 43-101 Technical Report on the

Wheeler River Project Athabasca Basin, Saskatchewan, Canada” dated August 8, 2023, with an effective

date of June 23, 2023, a copy of which is available on Denison's website and under its profile on SEDAR+

at www.sedarplus.ca and on EDGAR at www.sec.gov/edgar.

Based on the respective studies, both deposits have the potential to be competitive with the lowest -cost

uranium mining operations in the world. Permitting efforts for the planned Phoenix ISR operation

commenced in 2019 and are nearing completion with approval of the project ’s EA received from the

Province of Saskatchewan and CNSC hearing dates set in the fall of 2025 for Federal approval of the EA

and project construction license.

About Denison

Denison is a uranium mining, exploration and development company with interests focused in the

Athabasca Basin region of northern Saskatchewan, Canada. In addition to Denison’s effective 95% interest

in its flagship Wheeler River Project, Denison’s interests in Saskatchewan also include a 22.5% ownership

interest in the McClean Lake Joint Venture (“MLJV”), which includes unmined uranium deposits (with mining

at the McClean North deposit via the MLJV's SABRE mining method having commenced in 2025) and the

McClean Lake uranium mill (currently utilizing a portion of its licensed capacity to process the ore from the

Cigar Lake mine under a toll milling agreement), plus a 25.17% interest in the Midwest Joint Venture’s

Midwest Main and Midwest A deposits, and a 70.55% interest in the Tthe Heldeth Túé (“THT”) and Huskie

deposits on the Waterbury Lake Property. The Midwest Main, Midwest A, THT and Huskie deposits are

located within 20 kilometres of the McClean Lake mill. Taken together, Denison has direct ownership

interests in properties covering ~384,000 hectares in the Athabasca Basin region.

Additionally, through its 50% ownership of JCU (Canada) Exploration Company, Limited (“JCU”), Denison

holds additional interests in various uranium project joint ventures in Canada, including the Millennium

project (JCU, 30.099%), the Kiggavik project (JCU, 33.8118%), and Christie Lake (JCU, 34.4508%).

In 2024, Denison celebrated its 70th year in uranium mining, exploration, and development, which began

in 1954 with Denison’s first acquisition of mining claims in the Elliot Lake region of northern Ontario.

For more information, please contact

David Cates (416) 979-1991 ext. 362

President and Chief Executive Officer

Geoff Smith (416) 979-1991 ext. 358

Vice President Corporate Development & Commercial

Follow Denison on X (formerly Twitter) @DenisonMinesCo

Cautionary Statement Regarding Forward-Looking Statements

Certain information contained in this press release constitutes ‘forward-looking information’ within the meaning of the applicable United

States and Canadian legislation, concerning the business, operations and financial performance and condition of Denison. Generally,

these forward-looking statements can be identified by the use of forward- looking terminology such as ‘potential’, ‘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’ or ‘be achieved’.

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In particular, this press release contains forward-looking information pertaining to the following: expectations with respect to the EA

process, including the filing of the final EIS and the results and objectives thereof; expectations regarding regulatory reviews and

processes, including hearings with the CNSC Commission; and expectations regarding its joint venture ownership interests, including

plans for mining and the use of SABRE by the MLVJ, and the continuity of its agreements with its partners and third parties.

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 acti vity,

performance or achievements of Denison to be materially different from those expressed or implied by such 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 results 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 28, 2025 under the heading ‘Risk Factors’ or in subsequent

quarterly financial reports. 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.