Plants and Animals

Pyganodon lacustris Lake floater

Key Characteristics

The medium-sized (to 4 inches), elongate and very thin-shelled lake floater is characterized by a straight to gently curved ventral margin, low and narrow beak, and wide ridge extending to the bluntly pointed posterior end. Juvenile shells are yellow-green, becoming dark brown to black with age.

Status and Rank

US Status: No Status/Not Listed
State Status: SC - Special Concern (rare or uncertain; not legally protected)
Global Rank: GU - Unrankable
State Rank: SNR - Not ranked


CountyNumber of OccurrencesYear Last Observed
Benzie 2 2001
Charlevoix 2 2015
Cheboygan 5 2015
Leelanau 1 2009
Marquette 1 2010
Oakland 2 1925
Schoolcraft 1 2011

Information is summarized from MNFI's database of rare species and community occurrences. Data may not reflect true distribution since much of the state has not been thoroughly surveyed.


The lake floater inhabits lakes as well as rivers and streams with a slow-moving current (Watters et al. 2009).

Natural Community Types

  • Inland lake, littoral, benthic
  • Inland lake, pelagic, benthic
  • Mainstem stream (3rd-4th order), pool
  • Mainstem stream (3rd-4th order), run
  • Mainstem stream (3rd-4th order), riffle

For each species, lists of natural communities were derived from review of the nearly 6,500 element occurrences in the MNFI database, in addition to herbarium label data for some taxa. In most cases, at least one specimen record exists for each listed natural community. For certain taxa, especially poorly collected or extirpated species of prairie and savanna habitats, natural community lists were derived from inferences from collection sites and habitat preferences in immediately adjacent states (particularly Indiana and Illinois). Natural communities are not listed for those species documented only from altered or ruderal habitats in Michigan, especially for taxa that occur in a variety of habitats outside of the state.

Natural communities are not listed in order of frequency of occurrence, but are rather derived from the full set of natural communities, organized by Ecological Group. In many cases, the general habitat descriptions should provide greater clarity and direction to the surveyor. In future versions of the Rare Species Explorer, we hope to incorporate natural community fidelity ranks for each taxon.

Management Recommendations

Invasive zebra mussels infest the shells of native mussels, inhibiting movement and feeding, and sometimes result in the extirpation of entire communities (Schloesser et al. 1996). The spread of zebra mussel larvae and adults is best controlled by thoroughly cleaning boat hulls, trailers, scuba and fishing gear before moving between waterways.  As all unionid mussels are vulnerable to chemical pollutants (Bringolf 2007, Valenti et al. 2006, Wang et al. 2007)and heavy metals (Pip 1994, Valenti et al. 2005, Wang et al. 2007), limiting herbicide and pesticide use, industrial waste, mine drainage and urban run-off will benefit all species. Host fish populations on which glochidia rely must also be managed in order to preserve freshwater mussel diversity.  Dam building, dredging, bridge construction and other major habitat alterations often inhibit the movement of host fish. Such activities also cause the siltification of waterways, harmful to aquatic organisms in general, and should be followed up with monitoring and mitigation measures in order to minimize negative impacts.

Active Period

Gravid from first week of August to fourth week of May

Survey Methods

Visual and tactile search using scuba or glass-bottom buckets. Tactile search (by hand) is especially important where water turbidity and pebbles/rocks make visual detection difficult. After identification, live mussels should be planted back into the substrate anterior end down. Surveys should not take place after heavy rains or during periods of high water as these conditions can make detection much more difficult. Methods of documenting survey effort include: searching a large measured area, e.g. 128m2; taking multiple quadrat samples; and recording search time (person hours). For all methods, at least some excavation of substrate (by hand, 5-10cm down) should be done to detect buried mussels. Searching a large measured area or timed searches are generally better for detecting rare species and generating a species list than quadrat sampling. These two methods allow more types of microhabitats and a larger area to be covered. Quadrat sampling is better suited for documenting changes in density and other statistical analyses at the site level (Strayer and Smith 2003).

Glass-bottom bucket less than waist deep water

Survey Period: From first week of June to first week of October

Time of Day: Daytime
Water Level: Low Water Levels
Water Turbidity: Low Turbidity

SCUBA greater than waist deep water

Survey Period: From first week of June to first week of October

Time of Day: Daytime


Technical References

  • Bogan, A.E. 1993. Freshwater Bivalve Extinctions (Mollusca: Unionida): A Search for Causes.
  • Bringolf, R.B., W.G. Cope, C.B. Eads, P.R. Lazaro, M.C. Barnhart, and D. Shea. 2007. Acute and chronic toxicity of technical-grade pesticides to glochidia and juveniles of freshwater mussels (Unionidae). Environmental Toxicology and Chemistry 26(10):2086-2093.
  • Pip, E. 1995. Cadmium, lead and copper in freshwater mussels from the Assiniboine River, Manitoba, Canada. Journal of Molluscan Studies 61:295-302.
  • Scholesser, Don W., Thomas F. Nalepa, Gerald L. Mackie. 1996. Zebra Mussel Infestation of Unionid Bivalves (Unionidae) in North America. American Zoology 36:300-10.
  • Sethi, Suresh A., Andrew R. Selle, Martin W. Doyle, Emily H. Stanley, and Helen E. Kitchel. 2004. Response of unionid mussels to dam removal in Koshkonong Creek, Wisconsin (USA). Hydrobiologia 525:157-165.
  • Strayer, D.L. and D.R. Smith. 2003. A Guide to Sampling Freshwater Mussel Populations. American Fisheries Society Monograph 8, Bethesda. 103pp.
  • Valenti, T.W., D.S. Cherry, R.J. Currie, R.J. Neeves, J.W. Jones, R. Mair, and C.M. Kane. 2006. Chlorine toxicity to early like stages of freshwater mussels (Bivalvia: Unionidae). Environmental Toxicology and Chemistry 25(9):2512-18.
  • Valenti, T.W., D.S. Cherry, R.J. Neves, and J. Schmerfeld. 2005. Acute and chronic toxicity of mercury to early life stages of the rainbow mussel, Villosa iris (Bivalvia: Unionidae). Environmental Toxicology and Chemistry 24(5):1242-6.
  • Wang, N., C.G. Ingersoll, I.E. Greer, D.K. Hardesty, C.D. Ivey, J.L. Kunz, W.G. Brumbaugh, F.J. Dwyer, A.D. Robers, T. Augspurger, C.M. Cane, R.J. Neves, and M.C. Barnhart. 2007. Assessing contaminant sensitivity of early life stages of freshwater mussels (Unionidae): Chronic toxicity testing of juvenile mussels with copper and ammonia. Environmental Toxicology and Chemistry. 35pp.
  • Watters, G. Thomas, Michael A. Hoggarth, and David H. Stansbery. 2009. The Freshwater Mussels of Ohio. The Ohio State University Press, Columbus. 421 pp.