A top House Republican is charging that the Environmental Protection Agency secretly drafted highly detailed maps of U.S. waterways to set the stage for a controversial plan to expand regulatory power over streams and wetlands, a claim the EPA strongly denies.

Rep. Lamar Smith, R-Texas, chairman of the House Science, Space, and Technology Committee, released those maps on Wednesday, while firing off a letter to EPA Administrator Gina McCarthy voicing concerns over why they were created in the first place.

"These maps show the EPA's plan: to control a huge amount of private property across the country. Given the astonishing picture they paint, I understand the EPA's desire to minimize the importance of these maps," he wrote, in the letter obtained by FoxNews.com.

But an EPA spokeswoman said the maps, from the U.S. Geological Survey and Fish and Wildlife Service, do not depict which waters are subject to EPA control.

"Let us be very clear -- these maps have nothing to do with EPA's proposed rule or any other regulatory purpose," Liz Purchia said, noting they were initially created years ago and subsequently updated.

At issue is a proposal that Smith and fellow Republicans, as well as farmers and other groups, say could endanger private property rights by giving the EPA a say over temporary waterways like seasonal streams, under the Clean Water Act. That the agency had highly detailed maps drawn up has raised suspicion about their purpose.

"While the Agency marches forward with a rule that could fundamentally re-define Americans' private property rights, the EPA kept these maps hidden," Smith wrote in his letter. "Serious questions remain regarding the EPA's underlying motivations for creating such highly detailed maps."

He added: "The EPA's job is to regulate. The maps must have been created with this purpose in mind."

The high-resolution maps of each state depict a dense and veiny web of intertwining waterways. They're color-coded to distinguish everything from canals and ditches to reservoirs to marshes to various types of streams. The maps show permanent streams, but also those that contain water for only part of the year.

The EPA denied the maps were drawn to chart areas subject to the Clean Water Act. The agency said they were only drawn to identify the "extent and location" of waterways and other details.

In two letters to Smith, in late July and early August, EPA Deputy Assistant Administrator Nancy Stoner explained the documents were originally prepared in 2005, and updated last year with data from the U.S. Geological Survey.

"EPA is not aware of maps prepared by any agency, including the EPA, of waters that are currently jurisdictional under the CWA or that would be jurisdictional under the proposed rule," she wrote, adding that the maps would have to be even more detailed to be used for that purpose.

Decisions over whether the EPA has authority over "particular waters," Purchia said, are almost always made in response to requests. She told FoxNews.com the maps in question would have to involve ground surveys to actually reflect the proposed rule, which she called "prohibitively expensive."

But the map details would appear to dovetail with the type of waterways the agency is looking at regulating.

Since last year, the EPA has floated new rules that would define what kinds of waterways fall under its jurisdiction. The Clean Water Act already gives the EPA the ability to regulate "U.S. waters," but Supreme Court rulings have left the specifics unclear when it comes to waters that flow only part of the year.

To address that, the EPA and Army Corps of Engineers want to define that authority -- and are eyeing waterways deemed to have some significant connection to major rivers, lakes and other systems.

The EPA claims this does not expand its authority, and only clarifies it.

But detractors claim this is an opening for the EPA to claim authority over countless waterways, including streams that only show up during heavy rainfall. Critics warn this could create more red tape for property owners and businesses if they happen to have even small streams on their land.

A House science committee aide called the EPA maps "eye-opening" for those following the process.

"These are not everyday, run-of-the-mill maps -- these are highly detailed," the aide told FoxNews.com, adding that the agency had not previously disclosed the documents for public comment.

The committee only learned about the maps after hearing from the U.S. Geological Survey that the EPA was having them drawn up. Lawmakers subsequently asked then-EPA Deputy Administrator Bob Perciasepe about them at a hearing last month, and he agreed to release them.

Smith, in his letter, also questioned why the agency used taxpayer money to create the maps. He asked the agency to provide all documents related to its contract for the maps, turn over any other previously undisclosed maps, and extend the comment period for at least another two months.

Under the current plan, the comment period is projected to close on Oct. 20.