Lotus Lake Alum Treatment

Week of September 29, 2024

The Riley Purgatory Bluff Creek Watershed District has hired a contractor to treat Lotus Lake with aluminum sulfate (“alum”) to control algal growth. The treatment will be applied over four days during the week of September 29, 2024.

Alum is safe for aquatic life and is commonly used to improve water quality by reducing phosphorus availability in lakes. Alum works by binding to phosphorus in the water column and sinking to the lake bottom. Bound phosphorus is unavailable to algae, and the algae “starve.” The result is a lake with fewer algal blooms and improved water clarity.

Frequently Asked Questions

How soon can I use the lake after treatment?
People should stay out of a treatment area while the alum application is actively underway. Otherwise, there is no restriction on swimming or using lake water for irrigation.

How quickly will I see results?
Water clarity in the lake will likely improve dramatically within a few days. The alum will stay bound to phosphorus for years.

How can we extend the results of the treatment?
Reducing the amount of phosphorus and sediment entering the lake is key to extending treatment effectiveness. You can help by not dumping yard waste into the lake, picking up and disposing of dog waste in the trash, and reducing or eliminating fertilizer use.

Who do I contact with questions? 
Josh Maxwell, Water Resources Manager
(952) 607-6512 ext. 4
jmaxwell@rpbcwd.org

A boat similar to above will be used to apply the alum treatment to the lake.

Map of the alum treatment area on Lotus Lake.