The EPA has responded to concerns among Nebraska farmers and their Capitol Hill representatives about the agency's use of aerial surveillance to monitor livestock, saying the flights are to enforce federal laws regarding impaired watersheds such as rivers and streams.

An Environmental Protection Agency spokesman told FoxNews.com the agency has used the practice for nearly a decade a cost-efficient way for it and state governments to reduce the number of on-site inspections and focus on “areas of the greatest concerns.”

The flights are used across a swath of Midwest the agency calls Section 7, which is composed of Nebraska, Iowa, Kansas and  Missouri.

The flights recently attracted the attention of a bipartisan group of Senate and House members from Nebraska, who this week wrote the EPA with a list on nearly two dozen concerns.

 “Farmers and ranchers in Nebraska pride themselves in the stewardship of our state's natural resources. As you might imagine, this practice has resulted in privacy concerns among our constituents and raises several questions,” sid the letter signed by Nebraska Republican Reps. Adrian Smith, Jeff Fortenberry and Lee Terry, as well as Democratic Sen. Ben Nelson and GOP Sen. Mike Johanns.

The letter sent gave the agency until June 10 to respond.

A congressional aide familiar with the situation said part of the concern is Nebraska's Department of Environmental Quality has primary jurisdiction over such issues and Region 7 has only an oversight role. As a result, the flights might be undermining the state's effective enforcement. 

The aide also said there have been accusations that the EPA in some cases is levying fines based on aerial photos without on-the-ground inspections. 

The agency told FoxNews.com on Thursday that the flights -- along with state and other public records -- help monitors how animals eat and then excrete waste. But the EPA has never taken enforcement action only on the basis of the flights.