DES MOINES — A state commission has told lawmakers repeated cuts to the Iowa Department of Natural Resources threatened its ability to protect the state's air and water as the reductions have forced the agency to leave more than 100 positions vacant.

The Environmental Protection Commission's annual report to the Legislature noted the DNR's budget had been cut nearly in half, from $22 million in 2009 to $11.17 million in the current budget year.

The cuts have come amid increasing concerns about the state's polluted waterways.

"I think we're getting close to critical levels, given the significant loss of employees we've seen over the past eight to 10 years," said Chad Ingels, chairman of the commission, which oversees the DNR.

The agency is supposed to monitor about 9,500 animal feeding operations that house tens of millions of hogs, chicken and cattle. The DNR also enforces state and federal air and water regulations, licenses hunting and fishing and manages parks, forests and trails.

Agency cuts have come as state revenue shortfalls have forced lawmakers to repeatedly cut the budget. In just the past two years, the DNR's budget has been cut by 13 percent.

The cuts have prompted the DNR to close its forestry bureau, cut a dozen full-time jobs and keep about 70 positions vacant. In the past five years, the DNR also has cut an additional 40 jobs.

"We're getting spread thin enough that it's getting increasingly difficult to do everything that we currently do," said Chuck Gipp, the Iowa DNR director.

A budget proposal would keep the DNR's funding unchanged, but commission members have asked lawmakers to pass a supplemental salary bill to pay for increased employee costs.

Republican state Sen. Ken Rozenboom, R-Oskaloosa, said Friday he's "deeply concerned" about the DNR cuts. He noted the agency along with the Iowa Department of Agriculture have taken deeper cuts than some other departments.

"We obviously have budget problems in the state ... but there are limits to how much we can cut," he said.