Beaver Lake Eurasian Watermilfoil Monitoring and Control

Eurasian Watermilfoil Found in Beaver Lake
In October 2011, Eurasian Watermilfoil (EWM) was discovered near the boat ramp on Beaver Lake in Whitefish, Montana. An Aquatic Invasive Species (AIS) response team—off which the Whitefish Lake Institute (WLI) was a member—responded to the discovery for further investigation. Bottom barriers were placed over the identified patch and a control/eradication plan was developed by a multiple agency workgroup in which the City of Whitefish and WLI participated.

Why We're Concerned
If left untreated, EWM forms dense mats of vegetation on the surface of the water that can interfere with recreational activities such as fishing, swimming, and boating, and that threatens the health of the water body. The resulting effect can be the loss of recreational use, decline in ecosystem health, and a decrease in lakefront property values. EWM reproduces successfully and very rapidly, making it a threat to any water body it invades.

Ongoing Efforts
In the summer of 2012, snorkel surveys and subsequent diver dredging were conducted twice. Three pounds of EWM were removed by Ace Diving during the first effort, and twenty pounds were removed by Hanson Environmental during the second dredge event. No additional EWM occurrences were identified in the second snorkel survey.

The City of Whitefish funded an AIS program as recommended by WLI in 2013 and 2014. One component of the program is to survey and dredge any EWM plants found in Beaver Lake. Two combined snorkel survey and dredge events were completed in the summer of 2013, one at the beginning of July, and the other in mid-August. The entire littoral zone of Beaver Lake was visually surveyed by a snorkeler. Aside from one afternoon during which wake boats created shoreline turbidity, visibility was excellent during both inspections. Although no new areas of infestation were found, some re-growth was seen in the three patches that were dredged in 2012. In July of 2013, five pounds of EWM were removed and another one pound in August through diver dredging. Also in August, Fragrant Water Lily—another invasive species which had been introduced by a Beaver Lake lease-holder—was removed. A 10x10 patch of nearly 200 pounds of the well established plants was removed by hand. In 2014 a single snorkel and re-dredge was conducted with approximately one pound of EWM removed. With shoreline EWM appearing to be suppressed in Beaver Lake and only limited plants remaining, an annual snorkel and dredge is planned for 2015 and into the future.

Protecting Whitefish Lake from EWM and other AIS
Due to the close proximity of Beaver Lake to Whitefish Lake, WLI deploys a turbidity curtain to prevent fragments from moving downstream toward the lake. The curtain—provided by the Flathead Lakers—is installed at the outlet of Beaver Lake where Beaver Creek begins to flow. The curtain is deployed by WLI staff in the spring and removed in the fall on an annual basis. WLI also partnered with the Flathead Basin Commission to conduct a 100-point AIS presence/absence survey on Whitefish Lake. No EWM or other invasive plant species were found. EWM efforts will continue in the future.

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