Silver Lake Fen State Preserve

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State Preserves

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. 

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About the Land

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.

Fens 

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 calcium deposit resulting from oxidation of the calcium-rich groundwater. 

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Directions

  1. From the intersection of Highway 9 and Highway 86 on the west side of the town of Spirit Lake, take Highway 9 west for 9 miles to 110th Street. 
  2. Turn north (right) and go 0.5 mile to the preserve entrance. 
  3. Turn east (right) and follow the lane to the parking area (sign: Silver Lake Fen State Preserve).
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Plants

The saturated, peaty, and calcareous habitat of the fens supports a unique flora, as well as rare algae and zooplankton. 

Over 100 plant species can be found in the preserve, including some of the most rare in Iowa. Plant communities occur in three distinct zones on the fen. 

Discharge Areas

The “discharge areas” (elevated knobs where upwelling groundwater rises to the surface) are dominated by tall Phragmites reed and saw-tooth sun­flower. 

Sedge Mat Zone

The gentle slopes surrounding the discharge areas contain numerous small, shallow pools of water called “flarks” bounded by narrow ridges of peat called “strings.” The vegetation in this area, known as the “sedge mat zone,” is very short and is dominated by grasslike plants including:

  • Beaked rush
  • Common arrow-grass
  • Slender arrow-grass
  • Marsh muhly grass

Colorful forbs found in this zone include:

  • Grass-of-Parnassus
  • Brook lobelia
  • Lesser fringed gentian

The flarks contain aquatic algae and lesser bladderwort. 

Border Zone

Forming an outer ring on the lower edges of the fens is the “border zone,” an area of tall vegetation dominated by: 

  • Bulrushes
  • Sedges
  • Cattails
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Visitor Information

Other preserves in the vicinity include Cayler Prairie, Freda Haffner Kettlehole, and Ocheyedan Mound.

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