Invasive Species on Lake Onalaska
Lake Onalaska has numerous issues with invasive species. Among the problem species are: reed canary grass, Eurasian water milfoil, curly-leaved pondweed, purple loosestrife, faucet snails, and most recently, water lettuce.
An infestation of water lettuce, Pistia stratiotes, was reported to authorities in early October, 2015. The infestation was confined to the Brice Prairie shoreline bordering Lake Onalaska. An urgent call for volunteer help went out for Sunday, October 11, to remove as much of the infestation as possible before strong offshore winds would have broadcast the invader on Monday, October 12. Thirty to forty volunteers and agency staff worked hard through the day, found the source of the infestation, and removed every visible plant.
Although usually a problem in more southerly areas, an infestation of water lettuce in the Winona area of the upper Mississippi River survived through the 2011 winter before it was eradicated. Water lettuce is a PROHIBITED species in Wisconsin. The invasive species rule (Wis. Adm. Code ch. NR 40) makes it illegal to possess, transport, transfer, or introduce.
Chronology of the 2015 Brice Prairie Water Lettuce Infestation
- Tuesday October 6 - Jodi Lepsch (WDNR-Eau Claire) receives a report that water lettuce was found in Lake Onalaska. Lepsch notifies Scott Caven, Aquatic Invasive Species Coordinator with the River Alliance of Wisconsin, who is based out of the US Geological Survey&s Upper Midwest Environmental Sciences Center in La Crosse. Caven calls the person who reported the water lettuce - David Jensen - for more information. That evening, Caven monitors Lake Onalaska and confirms that water lettuce is in fact present. Caven collects 1 trash bag full of water lettuce and prepares to contact USFWS and other stakeholders the next morning (October 7th).
- Wednesday October 7 Scott Caven notifies the La Crosse and Winona District of USFWS and USFWS Headquarters that there is water lettuce in Lake Onalaska.
- Thursday October 8 - Scott Caven notifies WDNR AIS personnel about the water lettuce in Lake Onalaska and also monitors Lake Onalaska near the USFWS overlook on Brice Prairie, collecting 1 trash bag full of water lettuce. Brice Prairie residents and conservation club alerted through email list and word of mouth. (detailed update text)
- Friday October 9 - Scott Caven and Kendra Niemec of USFWS conduct airboat survey of Lake Onalaska, mapping lettuce occurrence with GPS. Distribution initially appears to be confined to Brice Prairie shoreline. Release site is located during the survey; they discover water hyancinth there as well. Weather forecasts predict high winds for Monday October 12 which would widely broadcast the large numbers of lettuce plants entrapped in lake-margin vegetation. Planning begins for volunteer and resource agency cleanup of high-risk distribution areas for Sunday, October 11. (detailed update text)
- Saturday October 10 - spot cleanup by residents along Brice Prairie shore; further assessment of distribution and call for volunteers. (detailed update text)
- Sunday October 11 - Cleanup effort by at least 25 vessels and over 40 persons documented...supplemented by substantial undocumented shore-based retrieval efforts. Many bags of plants removed, including all visible plants in at-risk-for-distribution area. Source of infestation investigated near "Tubes" walkout - law enforcement becomes involved immediately. Source mat removal begins. First La Crosse Tribune article, in morning edition, calling for volunteers. (detailed update text)
- Monday October 12 - High NW winds break up the nearshore vegetation mats that had been holding back lettuce plants. Small numbers of plants that were overlooked during the Sunday cleanup move east along the Brice Prairie shoreline, but winds do not distribute them offshore. Limited cleanup continues, but only in wind-protected areas.(detailed update text)
- Tuesday October 13. DNR surveys south and east shores of lake near spillways - no plants found. Survey and removal efforts continue all along Brice Prairie shore, Bell Island, and at source. (detailed update text)
- Wednesday October 14. USFWS continued cleaning up at the "source", finding ~50-75 more plants, including some large healthy ones under a dock. More surveys of outlying areas not turning up more plants. 8 plants found along Brice Prairie exposed shore, 8 more in the Brice Prairie channel. USFWS issues news release about water lettuce on Pool 7. (detailed update text)
- Thursday October 15. Strong afternoon winds with an offshore component again present risk of wider distribution. Shawn Giblin (Wi-DNR) surveys a huge amount of shoreline, mostly before winds developed, including French Island and its spillway, nicely tightening up our potential search area. 7 more plants found along Brice Prairie exposed shoreline, before winds developed. (detailed update text)
- Friday October 16. Water lettuce plant numbers found in surveys diminishing - 7 found inside Brice Prairie channel and only 2 along Brice Prairie exposed shoreline. More surveys on French Island turn up nothing. La Crosse Tribune publishes second article on the water lettuce infestation. (detailed update text)
- Saturday October 17. Only 1 plant found along Brice Prairie exposed shoreline and 1 at the end of the barrier island. Nothing found in another survey of Sailing Club and Rosebud Island. Onshore winds forecast for next few days should preclude further distribution for awhile. (detailed update text)
- Sunday October 18. Winds turn onshore. 2 more plants found along Brice Prairie shoreline. (detailed update text)
- Monday October 19. Volunteers find 10 more plants in the Brice Prairie channel. Onshore winds are precluding any escapes, and starting to pile large floating mats of uprooted wild celery along the exposed shoreline. Two plants found on French Island in the bay by Nelson Park landing. (detailed update text)
- Tuesday October 20. 44 more water lettuce plants found in the upper Brice Prairie channel, between the Fred Funk landing and the source at the tubes. Two plants found at the eastern end of the Brice Prairie channel. No plants found in foot survey of upper/lower spillway landings, culvert, dike, and shoreline 100 yards south toward Round Lake on east side. (detailed update text)
- Wednesday October 21. 10 more water lettuce plants found in the lower Brice Prairie channel, mostly at the east end of the barrier island. No plants found in survey of Upper Spillway area. (detailed update text)
- Thursday October 22. 13 more water lettuce plants found in the Brice Prairie channel. No plants found along Fishermen's Road on French Island or Onalaska Spillway area. (detailed update text)
- Friday October 23. Two more water lettuce plants found in the lower Brice Prairie channel. (detailed update text)
- Saturday October 24. Five more plants found, 3 in the upper Brice Prairie channel and two on the lower channel. Light winds parallel to or slightly offshore. (detailed update text)
- Sunday October 25. Three more plants found, 1 east of FWS Outlook. Onshore winds (detailed update text)
- Monday October 26. One plant found at east end of Brice Prairie barrier island. (detailed update text)
- Tuesday October 27. No plants in lower Brice Prairie channel today!. (detailed update text)
- Thursday October 29. Five plants found in lower Brice Prairie channel. (detailed update text)
- Friday November 6. There are still occasional water lettuce plants being found along the Brice Prairie Channel, but with recent wind directions it is unlikely that any have escaped across Lake Onalaska and beyond. Plan for removing any surviving plants from groundwater "springs" over the winter and for spring/summer removal of plants germinating from seed banks. Waterfowl migration in full swing! (detailed update text)
- Thursday November 12. A few plants still being found in the lower Brice Prairie Channel. Strong NW winds today but a thorough search of the lower BP Channel yesterday should make it unlikely that any plants will escape. Quite a few dead ducks along the shoreline, with many eagles on the lake feasting on waterfowl weakened by trematodiasis. (detailed update text)
Photos from the October 11, 2015 "Water Lettuce Roundup"