In 2001, species lists were compiled for the county's islands. Snake Island had 156 species, Cana Island had 111, Hat Island 22, Chambers Island 398, Adventure Island 58, Little Strawberry Island 44, Jack Island 28, Horseshoe Island 49, Sister Island 6, Spider Island 42, Plum Island 259, Detroit Island 25, Pilot Island 40, Washington Island 626, Hog Island 34, Rock Island 333, and Gravel and Fish islands were devoid of plant life. In particular, Washington Island is one of only two places in Wisconsin where the fern "Asplenium viride" (green spleenwort) is found. In 2006, 60 species of aquatic plants or macrophytic algae were found in Clark Lake and nearby upstream, including spotted pondweed, "Potamogeton pulcher", which is endangered in Wisconsin. In 2017, 9 species of aquatic plants were found in the Forestville Millpond, also called the Forestville Dam or Forestville Flowage. In 2019, 25 miles of roadsides were surveyed for invasive species. A county-wide electronic map of Japanese knotweed, "Phragmites", teasel, and wild parsnip infested locations is updated annually. Locations of other problem species have also been documented. Yearly fluctuations in lake levels alternately kill off vegetation during periods of high water and promote succession during times of low water. Even during times of high water when low-lying plants are inundated, the populations may persist uphill by clonal expansion and spreading their seeds. Lake Michigan has more diverse shoreline vegetation than Lake Ontario, which has a more stable water level due to human intervention. Without the changing lake levels the shoreline would be dominated by woody plants or highly competitive and even invasive water-loving species such as cattails, reed canary grass, or purple loosestrife. Wet meadows like this one thrive when flooding does not occur often enough to allow emergent vegetation to prevail but is still too frequent to allow the establishment of trees and shrubs. Orchids  Although The Ridges Sanctuary is home to wild orchids, it also operates an orchid restoration project to cultivate and introduce rare orchids into otherwise natural plant communities. 25 native orchid species are currently kept at the Ridges. A 1998 survey of wild, native orchids was carried out in response to continued theft of the sanctuary orchids. 28 species were identified. Potatoes  The U.S. Potato Genebank at the Peninsular Research Station just north of Sturgeon Bay is the world's second largest living collection of wild potatoes with 65 wild species in 2010.