Yellow Loosestrife

Yellow Loosestrife is present on Cranberry Lake

We have another invasive species on our lake that was discovered in August of 2013 by Jim and Terrie Hanrahan. It has been identified as Yellow loosestrife (YL). The plants were first located on the small bog island northeast of Cranberry Island. There is a much larger area on the opposite shore northeast of the island. Other areas are located in the bay to the north of the island just before the channel, and in the bay at the far northern end of the lake.

YL is a 3 to 6 foot tall perennial with yellow flowers that bloom in mid to late summer. It forms dense stands in wetlands and crowds out native vegetation. The plant apparently spreads both by seed and from rhizomes.

Each year ERCLA volunteers monitor YL locations and note sites with a GPS waypoint. Our volunteers are Jim and Terrie Hanrahan, Chrysa Murphy, and Carole Linn. We can always use more volunteers, so please consider offering a little of your time. It’s really a pleasant task cruising the shoreline, looking for loosestrife, and marking its location on a GPS. We’ll provide all the training and supplies. Click here to volunteer.

A map showing the location of yellow loosestrife on the Eagle River Chain in 2016 is available. Click here to view the map.

Click here for a Yellow loosestrife info sheet.



Since the initial appearance date of the plant and the rate at which it is spreading are unknown, a monitoring project has been initiated to help determine just how great a threat this invasive is to the lower Eagle River Chain of Lakes. This project was developed with the assistance of Quita Sheehan, Vilas County Lake Conservation Specialist, and botanist.

Cranberry Lake riparians Jim and Terrie Hanrahan identified specific YL plants in the bog islands and marked them with stakes. They monitored the growth of YL, specifically from rhizomes. In addition, they counted the number of stalks and the number of blossoms of YL on the bog islands. These numbers will be compared to counts in future years. All data is recorded, and photographs are taken to substantiate the findings.





The second aspect of the monitoring project involved the establishment of test plots. Riparians on Cranberry Lake volunteered to host a five year shoreline study of YL. In August of 2014, a study area which was known to contain YL was established near the dock on their property. Quita Sheehan identified all plant species present in 8 transects within the study area and determined the percent coverage of each species within the subplots. In 2019, plants in these same 8 transects will once again be identified and the respective proportions noted. A comparison of the number of plant species and their percent coverage between 2014 and 2019 will help determine the spread of YL over the 5 year time-period and the extent to which native plants may have been reduced.