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Update: All scheduled Curlyweed Pondweed treatments were completed on May 17th.


AIS Control

Please check this page for the most up-to-date AIS lake treatment information!

Aquatic Invasive Species (AIS) Control - Plants

The Riley Purgatory Bluff Creek Watershed District (RPBCWD) conducts aquatic plant surveys for multiple lakes on a rotational basis. The purpose of the surveys is to monitor native and non-native plant populations to inform decisions about aquatic plant management for lake health. The District does not intentionally manage aquatic plant populations for recreational benefit.

Curlyleaf Pondweed (Potamogeton crispus) and Eurasian Watermilfoil (Myriophyllum spicatum) are the most problemative invasive non-native aquatic plants in the District. The District uses herbicide treatments to control these Aquatic Invasive Species (AIS) to a level that allows native plant populations to increase.

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This page will be updated as new information, including treatment dates, becomes available. Please bookmark this page and check back for updates.

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2023 Lake Herbicide Treatments by RPBCWD

RPBCWD applies for a permit from the Minnesota DNR to control aquatic invasive species in a lake. If a permit is granted, RPBCWD will work with a contractor to apply aquatic herbicide to control aquatic invasive plants in that lake. Treatments managed by RPBCWD occur at no cost to residents.

The decision to treat a particular lake is based upon aquatic plant surveys that determine the distribution and density of target invasive species. See schedule below for lakes considered for treatment this year.




[updated 5/19/2023 at 8 a.m.]

LAKE NAME Target invasive species Herbicide name Location(s) Size of treatment Treatment timing*
Mitchell Lake Curlyleaf Pondweed Flumioxazin See map 12.9 acres May 17 (Wednesday)
Lake Susan Curlyleaf Pondweed Flumioxazin See map 5.3 acres May 17 (Wednesday)
Red Rock Lake Curlyleaf Pondweed Aquathol See map 13 acres May 17 (Wednesday)
Rice Marsh Lake Curlyleaf Pondweed Diquat N/A (no 2023 treatment) N/A No treatment in 2023
Lake Riley - 1 Curlyleaf Pondweed Diquat See map 22.2 acres May 17 (Wednesday)
Lake Riley - 2 Eurasian Watermilfoil ProcellaCOR/Diquat See map (pending) 16 To be determined
Staring Lake Eurasian Watermilfoil ProcellaCOR/Diquat See map (pending) 10 To be determined
Lotus Lake Eurasian Watermilfoil ProcellaCOR/Diquat See map (pending) 22.2 To be determined

*Dates may change due to weather. See "Timing" below.




Treatments are scheduled during optimal weather conditions (low wind, water temperature near 60 degrees F). Dates of treatment may change due to changes in weather or other unforseen circumstances.

All Curlyleaf Pondweed treatments must occur before June 1st per MnDNR regulation to protect native aquatic plants. Eurasian Watermilfoil treatments typically occur mid June to mid July when the plant is most actively growing.


For the most recent information about treatment status, please check this webpage.

For other AIS or water resources management questions, contact:

Josh Maxwell 
952-607-6512 Ext. 4

Aquatic Plant Regulations

MnDNR regulates aquatic plant management in public bodies of water. A permit is usually required to manage aquatic plants. For more information visit MnDNR Aquatic Plant Management.

Herbicide Information

Selection of herbicides is based upon a number of factors including target invasive species, previous treatments, lake characteristics, cost, or other variables. After herbicide treatment, the Minnesota DNR recommends not using the lake water for these activities for the listed number of days.

Activity Aquathol
(active ingredient: endothall)
Diquat Flumioxazin ProcellaCOR
Swimming 1 day 1 day 0 days 0 days
Drinking (people and pets) 3 days 3 days 0 days 0 days
Irrigation 7 days 5 days 5 days 5 days