Alliant Energy: Receives approval for environmental controls project to improve air quality at Edgewater Generating Station

Media Contact: Steve Schultz (608) 458-3285

Approximately $150 million investment will reduce nitrogen oxide emissions

MADISON, WI – May 11, 2010 – Wisconsin Power and Light Company (WPL), a subsidiary of Alliant Energy Corporation (NYSE: LNT), has received oral approval from the Public Service Commission of Wisconsin (PSCW) to install additional emissions reduction technology at Edgewater Generating Station Unit 5 in Sheboygan, Wisconsin.

Pending a written Order from the PSCW, the decision authorizes WPL to build a Selective Catalytic Reduction (SCR) system. The approximately $150 million investment is the next step in WPL’s efforts to reduce nitrogen oxide (NOx) emissions at Edgewater Unit 5 to comply with Wisconsin’s Reasonably Available Control Technology (RACT) requirements.

“Our emission control projects at Edgewater are an integral part of our company’s commitment to protecting the environment and providing both our current and future generations of customers with safe, reliable and environmentally responsible energy,” said Barbara Swan, President – WPL. “We believe the SCR at Edgewater Unit 5 further demonstrates our commitment to the environment and the air quality around our plants.”

WPL anticipates the SCR at Edgewater Unit 5 will be ready for commercial operation in late 2012.

Alliant Energy is an energy-services provider with subsidiaries serving approximately 1 million electric and over 412,000 natural gas customers. Providing its customers in the Midwest with regulated electric and natural gas service is the company’s primary focus. Wisconsin Power and Light, the company’s Wisconsin utility subsidiary, serves approximately 460,000 electric and 180,000 natural gas customers. Alliant Energy, headquartered in Madison, Wis., is a Fortune 1000 company traded on the New York Stock Exchange under the symbol LNT. For more information, visit the company’s Web site at

This press release includes forward-looking statements. These forward- looking statements can be identified as such because the statements include words such as approximately, anticipates or other words of similar import. Similarly, statements that describe future plans or strategies are also forward-looking statements. Such statements are subject to certain risks and uncertainties that could cause actual results to differ materially from those currently anticipated. Actual results could be affected by such factors as:

— unanticipated construction issues, delays or expenditures, including increased costs of labor, materials and equipment;

— failure of equipment and technology to perform as expected;

— state regulatory actions or local government actions which delay, prevent or alter the proposed plans, including delays in the regulatory approval WPL’s plan to purchase an interest in Edgewater Unit 5;

— current or future litigation, regulatory investigations, proceedings or inquiries that could impede the implementation of WPL’s plans;

— changes to WPL’s access to capital markets; and

— economic conditions in WPL’s service territory.

These factors should be considered when evaluating the forward-looking statements and undue reliance should not be placed on such statements. The forward-looking statements included herein are made as of the date hereof and Alliant Energy and WPL undertake no obligation to update publicly such statements to reflect subsequent events or circumstances.