Project Description & Outcomes

The first phase of the Forest Lake Alum Treatment was completed during the week of September 25th to 29th, 2023. The District will monitor project effectiveness in 2024 in order to determine alum dosing requirements for a second alum application in 2025.

The Forest Lake Alum Treatment Project is a milestone project in achieving Forest Lake’s water quality goals. The Comfort Lake-Forest Lake Watershed District has worked with many partners to construct water quality projects for more than a decade. With the critical support of the City of Forest Lake and the Forest Lake Lake Association, these projects have led to a significant decline in phosphorus entering the lake. The watershed district targets phosphorus, because in excess amounts, it causes algae blooms and lowers water quality. Less phosphorus is entering the lake, but a project is needed to address the phosphorus that is already in the water.

The lake is treated with alum which binds to phosphorus and makes it unavailable for algae growth. Alum is a non-toxic water quality treatment that will result in a cleaner and clearer Forest Lake.

The alum treatment took place in September 2023. The Watershed District will monitor the lake after the treatment to measure success and determine if a second application is needed in 2025. 

Project Status


Project Outcomes

527 lbs/yr phosphorus removal 


Clean Water Fund Grants: $533,600

CLFLWD Grant Match: $133,400

Total Project Budget : $667,000

Lifecycle cost:
$100 per pound of phosphorus removed
(What does this mean?)


Fall 2023: Alum application #1

2024: Effectiveness Monitoring

Fall 2025: Potential alum application #2

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