Eurasian Watermilfoil Detected on Manitowish Lake and Channel to Alder

On July 15 an AIS Volunteer discovered floating fragments of Eurasian Watermilfoil (Myriophyllum spicatum) on Alder Lake and rooted plants in the channel towards Manitowish Lake. The MWLA board was immediately in contact with our county conservation specialist to discuss further plans for surveying and monitoring. Following the discovery, an incident report was filed with the WDNR and the WDNR, Vilas County Land and Water, and the North Lakeland Discovery Center conducted surveys on August 9. The surveys included visually searching from the boat, snorkeling, and rake-throws on Alder Lake and the channel from Alder to Manitowish Lakes. The survey on Alder Lake did not discover any rooted plants or floating fragments, however the survey on the channel discovered three medium colonies and 27 other locations of rooted plants.

During the surveys, samples were collected and pressed to be submitted as vouchers to the state herbarium. While surveying, the colonies and rooted plants were explored to determine if any hand-pulling could be done this year, but the plants were brittle and breaking up, a common sign that their season is ending. At the end of summer Eurasian watermilfoil begins to die back as the waters cool off. Pulling efforts with brittle plants can cause more harm than good because many pieces and filaments of the plant break apart, becoming suspended in the water and drifting off to spread new populations of plants throughout the waterbody.

Each year, the Woods and Water team at NLDC survey 3 to 4 lakes of the chain on a rotating basis with the WDNR lakes protocol for Early Detection Rapid Response program. This rotation covers all lakes every 3 years. The protocol looks for early detection of many different AIS (aquatic invasive species) and is a snapshot of the waterbody. The lakes are surveyed at the end of summer and this year included Manitowish, Clear, and Little Star. Unfortunately, Eurasian watermilfoil was also discovered at 4 of the 5 sample sites on Manitowish Lake.

The WDNR and MWLA have been working closely with the North Lakeland Discovery Center to determine a plan of action for next year. There is a WDNR Early Detection Rapid Response grant program that this project will be eligible for, and the grant will be submitted this fall. Eurasian watermilfoil is a very invasive submerged plant that can be extremely aggressive and spreads quickly. Manitowish Lake was last surveyed with the EDRR protocol in 2020 and no Eurasian watermilfoil was found. This species had not ever been detected as growing on the chain and this is the first discovery of it, however it has been identified in 42 other lakes in Vilas County.