Johnson County’s growing thirst for water is endangering the Kansas River, Dave Murphy said.

A proposed dam on the river near DeSoto to help quench that thirst is “unethical,” said Murphy, Friends of the Kaw riverkeeper.

But water officials say they have not made a final decision about building a structure to ensure adequate flow to an intake at the defunct Sunflower Army Ammunition Plant.

“I would hope the water district really knows this is something that’s not viable, environmentally or recreationally or from a navigability standpoint,” Murphy said Wednesday. “It’s unethical to do this.”

Byron Johnson, general manager of Johnson County Water District No. 1, said officials were looking at many options for water, including a dam.

“There’s engineering work going on, but there’s no decision,” Johnson said. “I’m not sure what we’re going to do.”

The water district serves 15 cities and one rural district in Johnson County. In June, the district made two applications to build a dam on the Kansas River. One would locate a dam about 1.5 miles northwest of DeSoto; the other would be about 3 miles west and northwest of the city.

Johnson said the applications were part of an engineering study to increase the county’s water treatment capacity by 50 million gallons a day. Johnson County already has the ability to take 165 million gallons a day from the Kansas and Missouri rivers. During the summer, the county treated as much as 130 million gallons a day.

The additional capacity is needed “strictly because of growth” in the county’s population, Johnson said.

Murphy said a better option  one that wouldn’t block boats and canoes traveling down the river, and wouldn’t affect fish and other wildlife living in and around the river  would be to construct a “well field” in the floodplain along the river. That would involve drilling many wells, dozens or hundreds depending on how well they produce, from which to collect groundwater seeping from the river.

Johnson said engineers were looking at that option. They’re also looking at pulling additional water from the Missouri.

Without providing cost estimates, however, he said building a dam “would be the most economical (choice), there’s no doubt about that.”

Murphy wasn’t so sure.

“That cost difference … turns out to be pennies a month for ratepayers over the 40 years it would be paid for,” Murphy said. “The cost is insignificant.”

Johnson said the county hadn’t applied to the U.S. Army Corps of Engineers to approve a dam; the corps must give permission before the project could go forward. A spokeswoman for the Division of Water Resources said there was no deadline for the state’s decision.

Murphy said there was one official dam along the Kansas River: the Bowersock Dam in Lawrence, bigger than what Johnson County officials have proposed at DeSoto. There also are several “weirs” (miniature dams): two in Topeka and one at Mill Creek. No more are desired, Murphy said.

“They are going to severely damage this river,” he said. “We’ve got some big battles to fight.”