Update 5/11/26: All four lakes, Red Rock, Sysan, Riley, and Mitchell were treated for CLP on May 7th, 2026. 

Weather permitting, Red Rock and Susan will be treated for curly-leaf pondweed on Thursday, May 6th. Riley and Mitchell treatment dates are TBD. Follow rpbcwd.org/AIS-control for updates under "2026 Lake Treatment Information".

RPBCWD staff recently completed delineation surveys for Curly-leaf pondweed on selected lakes within the District.  The purpose of these surveys is to monitor native and non-native plant populations to inform decisions about aquatic plant management for lake health.  CLP is one of the most problematic invasive species in the District. The District uses herbicide treatments to control this Aquatic Invasive Species (AIS) to a level that allows native plant populations to increase. The abundance of CLP on Mitchell, Red Rock, Riley, and Susan lakes were high enough to warrant herbicide treatment.

The size of treatment areas is limited by the MN DNR and will be located in the areas of highest CLP density. The exact timing of treatments is determined the day before based on predicted weather conditions and contractor availability. 

Postcards have been mailed to residents immediately adjacent to treatment areas, If your shoreline area is within 150 feet of a curlyleaf pondweed or Eurasian water milfoil treatment area, and you'd like to opt out of treatment, contact Shauna Capron at scapron@rpbcwd.org or 612-791-9085. Click on a map below to see where treatments will be taking place:

Red Rock Lake Treatment MapMitchell Lake Treatment MapLake Susan Treatment MapLake Riley Treatment Map

Water Use Restrictions

In addition to treatment locations, there are water use restrictions to be aware of post-treatment. 

Susan and Riley will undergo an Endothall treatment. After an Endothall treatment, the DNR recommends not using the water for drinking for 5 days and for irrigation for 7 days. There are no restrictions for swimming.

Red Rock and Mitchell will undergo a Flumioxazin treatment. After a Flumioxazin treatment, the DNR recommends not using the water for irrigation for 5 days. There are no restrictions for swimming or drinking water. 

Did you know aquatic plants are protected?

Aquatic plants are essential to lake health and their management is regulated by the MN DNR. Learn more about aquatic plant regulations from the DNR. Also, check out our Aquatic Plant Protection handout.