The district is pursuing a whole-lake treatment of aluminum sulfate (Alum) to reduce the internal lake loading of phosphorus.  Alum binds to phosphorous making it bio-unavailable to plants and algae.  This project was selected based on the advice of the SEWERPC report, and industry experts, as having the highest priority and return-on-investment.  The district is seeking financing from a 75% reimbursement  WDNR Surface Water Grant and a loan from BCPL to be repaid through normal district member special assessment revenue. 


Excess phosphorus is the leading cause of water quality problems in Lake Denoon and the sediment phosphorus has accumulated over decades.  Lake Denoon is unique in that it has a relatively small watershed with no continuous outflow which means that inbound nutrients remain and don't easily flush out.   These characteristics make Lake Denoon particularly well suited for Alum and the benefits of this project are expected to last for 10-20 years.  This is the first action taken, in the the lake's history, to address the nutrient pollution already in the lake. 

Clean Boats Clean Waters (CBCW)

This is a program where trained inspectors work at the boat launches, inspecting visiting trailers and boats as they enter our lake to reduce spread of Aquatic Invasive Species (AIS).  The inspectors interview visiting boaters and educate them about AIS and best practices when moving from lake to lake.  

This program has been determined to be highly effective in slowing the spread of AIS including Starry-Stonewort. 

The LDLD Board of Commissioners applied for, and was awarded a 75% matching grant to fund this program.  This means that we can pay individuals to work the launches.  We are currently looking for help in administering and working the program.  Please consider helping by contacting any Commissioner or sending an email to


A few dedicated volunteers are monitoring the water quality in the lake and its tributaries through the CLMN and WAV programs.  We measure temperature, clarity, and chlorophyll-A in the lake and dissolved oxygen, clarity, volume, and macroinvertebrates in the tributaries.  These data are uploaded into the SWIMS database to track our lake's changes over time which helps us target measures to mitigate eutrophication.


Please email if you are interested in learning more.

Sonar Treatment - This project has concluded.

A whole-lake treatment with Sonar (Fluridone) has been completed in 2019/2020.  This material was determined by the LDAA and LDLD to be the best option for controlling the two most prominent invasive weed species Eurasian Water Milfoil (EWM) and Curly Leaf Pondweed (CLP).   The project consisted of a primary application conducted in June 2019 with a booster application in mid summer and a spring 2020 booster. The selected vendor was  Marine Biochemists. The project was financed through a loan which will be repaid with normal LDLD special assessment revenues.  Financing was secured through the Board of Commissioners of Public Lands (BCPL).  The DNR approved our request and has issued our permit.  The initial product application was conducted on 6/3/19.  The treatment worked as expected with good control of EWM growth.  In the first year, control of EWM was very successful with no plants visible above the water surface to be shredded by boat props.  We were able to maintain the Sonar product in-lake level at or above 2 parts per billion (ppb) after the initial application as recommended.  As called for in the plan, we took a series of residual measurements and the Sonar product levels had fallen below 2ppb so our vendor conducted booster applications on 8/14/19 & 11/4/19. 

Update 2020

After approval of our 2020 permit, the final booster Sonar application was conducted on 6/9/20.  Although the EWM has successfully been controlled, the CLP has taken advantage of the available nutrients and space in the absence of EWM and is as rampant as the EWM last-year.  Hopefully, the boost of Sonar will slow the CLP spread.  CLP will naturally die off in mid-summer.

As a final step in the project, our vendor has conducted an aquatic plant survey.  The survey report can be found here and has been submitted to the DNR.  The report will inform the DNR as to what abatement remedies will be recommended / permitted next year.

Project Plan  |  DNR Fluridone Factsheet  | Project Files