Disappointing news. Zebra mussel larvae have been confirmed in Rainy Lake by the Minnesota Department of Natural Resources (MNDNR). The larvae were found in four of five water samples taken in July 2021, suggesting that there is a reproducing population in the lake according to MNDNR. This follows on an unconfirmed report of larvae in 2020 by a member of the public. Locations of adult reproductive colonies have not yet be located or confirmed. Rainy Lake straddles the Ontario-Minnesota border and flows downstream via the Rainy River to Lake of the Woods. This follows equally concerning confirmations by MN DNR in 2019 and 2020 of zebra mussel larvae at sites in the southern portion of Lake of the Woods.
The zebra mussel larvae were all found outside of the US National Park - Voyageurs National Park, which occupies about one-third of the lake. The Park has an intensive water sampling program which should help determine the extent of spread in Rainy Lake.
In Lake of the Woods, zebra mussel larvae were first detected by MN DNR in several locations of the southern basin in late 2019 and again in 2020. 2021 results are not in yet from Minnesota DNR. To date no reproductive colonies have been located in Lake of the Woods. Reportedly, Ontario Ministry of Natural Resources and Forestry will be conducting sampling
For further information see the MNDNR press release:
https://www.dnr.state.mn.us/news/2021/09/01/zebra-mussel-larvae-confirmed-rainy-lake-st-louis-county