Under Iowa's floodplain management program, various development activities within the floodplains of rivers and streams are regulated. Included are channel changes and the construction of dams. Currently, the DNR has designated 246 reaches of streams and rivers throughout Iowa as Protected Streams, including the coldwater trout streams of northeastern Iowa. For streams that are not Protected Streams, proposals for channel changes are reviewed to insure the proposal will not have an adverse impact on habitat. The review process often results in requirements for mitigation or, in some cases, disapproval of the channel change.
Dams can affect both the habitat and hydrology of a stream.
The pool formed by a dam can inundate natural channel habitat, and the flows downstream of a dam can be affected by the storage and evaporation of water behind the dam. The vast majority of dams constructed in Iowa are small dams constructed across small upland streams or drainageways and have no adverse impact on habitat or flow. Typical requirements are provisions for passing low flows through the dam, provisions for passage of fish, or provisions for maintaining adequate levels of dissolved oxygen downstream of a dam.