Water rarely flows in one of the streambeds — it really seems to be little more than a small ditch — that Dean Lemke points out to a visitor on his 800-acre farm in Dows, Iowa.

“I wouldn’t even call it a stream,” he said. “There is only water flow in it when it rains.”

Mr. Lemke is a former Iowa state government official who supervised water-quality programs. He is also a fifth-generation farmer who grows corn and soybeans on his acreage, about 75 miles north of Des Moines, and he has never worried that the government would be concerned about that small ditch.

But that may soon change.

The Environmental Protection Agency is set to issue regulations that farmers like Mr. Lemke say may require them to get permits for work for which they have long been exempt. The E.P.A. says the new rules are needed to clarify which bodies of water it must oversee under the federal Clean Water Act, an issue of jurisdiction that the agency says has been muddled by recent court rulings. Opponents say the rules are a power grab that could stifle economic growth and intrude on property owners’ rights.

There is no timetable for when the rules will be released. But if the agency expands its jurisdiction over streams like the one on Mr. Lemke’s farm, he and other farmers say, the move could prove costly by requiring farmers to pay fees for environmental assessments and to get permits just to till the soil near gullies, ditches or dry streambeds where water only flows when it rains. A permit is required for any activity, like farming or construction, that creates a discharge into a body of water covered under the Clean Water Act or affects the health of it, like filling in a wetland or blocking a stream.