Silver Lake Fen is a 10-acre preserve containing a series of unusual spring-fed, boggy, hillside wetlands known as “fens.” It is located on the southwestern shore of Silver Lake in Dickinson County in the “Lakes District” of northwest Iowa, 3 miles southwest of Lake Park and 15.5 miles west of Spirit Lake. The area was purchased by the Iowa Conservation Commission in the early 1940s. Water from some of the springs was collected in a pond created for the rearing of fish. Recognition of the unique natural features of the site resulted in its dedication in 1972 as a biological and geological state preserve.
Silver Lake is a glacial lake within the Des Moines Lobe, a landform region of north-central Iowa that was last covered by ice 12,000 to 14,000 years ago. Silver Lake Fen occupies a north-facing slope on the shore of Silver Lake. The lake and the fen are clustered among knobby hills characteristic of the Bemis end moraine of the Des Moines Lobe glacier. Three fens are found at Silver Lake. The large fen on the northwest part of the preserve is the one most often visited owing to its easy accessibility. Portions of the other two fens in the eastern part of the preserve extend slightly into adjacent private land that is leased by The Nature Conservancy. The largest fen, about 1.2 acres in size, is developed on a mound of decomposed peat approximately fifteen feet deep. Hydrologically, the fens are saturated by constant flow of cold, highly calcareous, upwelling groundwater. The fen is underlain in many areas by deposits of “tufa,” a porous