Skip to content
alert icon

Update: AIS lake treatments have finished for 2023.


AIS control

RPBCWD controls invasive aquatic plants to benefit native aquatic plants, which are important for lake health.

RPBCWD does not control invasive aquatic plants for recreational purposes. If you're considering control of aquatic plants along your shoreline, you likely need a permit for aquatic plant management from the Minnesota DNR.

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.

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 6/26/2023]

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 N/A N/A (no 2023 treatment) N/A No treatment in 2023
Lake Riley - 1 Curlyleaf Pondweed Diquat See map 9 acres May 17 (Wednesday)
Lake Riley - 2 Eurasian Watermilfoil N/A Decided not to treat due to plant survey results N/A No treatment in 2023
Staring Lake Eurasian Watermilfoil N/A N/A (no 2023 treatment) N/A No treatment in 2023
Lotus Lake Eurasian Watermilfoil Diquat See map 22.92 June 15 (Thursday)

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

Icon_alert_black.png Check back for updates

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

Depending on your device settings, you may need to refresh your browser/reload the page to see updated information.

Subscribe to Lake Notifications

New! E-notifications for lake treatments to begin in 2024.

* indicates required
I would like email notifications for District-led activities for these lakes:
Check a box to receive lake-specific notifications.

treatment Timing

RPBCWD staff only know the general timeframe of a treatment until weather predictions become more precise and lake water temperatures reach treatment standards. Actual treatments dates are typically selected the week before treatment, however applicator availability, MnDNR permit approval, or abrupt weather changes may affect scheduling or not allow us to determine exact dates until shortly before treatment.

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. 


Curlyleaf Pondweed (CLP)

All Curlyleaf Pondweed treatments must occur before June 1st per MnDNR regulations.  to protect native aquatic plants. The herbicides most commonly used to control CLP are detrimental to native aquatic plants, which typically begin growing after June 1st.


Eurasian Watermilfoil (EWM)

Eurasian Watermilfoil treatments typically occur mid-June to mid-July when the plant is most actively growing.

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 and MnDNR Aquatic Plant Regulations.

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 None None None None
Drinking (people and pets) 3 days 3 days None None
Irrigation 7 days 5 days 5 days 5 days




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