Cascade Water Alliance (Cascade) owns and operates the Lake Tapps Reservoir. Milfoil is found in most Northwest lakes and has been in Lake Tapps for decades. Cascade has no legal obligation to address milfoil; however, Cascade believes treating milfoil keeps the reservoir healthy. Cascade has treated and addressed milfoil management annually since 2010.
Based on a milfoil survey and information received from residents throughout the year, Cascade completed the Phase 1 treatment milfoil treatment on June 22, 2026, and Cascade plans a Phase 2 treatment the week of Aug 10. The areas designated to receive treatment in Phase 2 are marked on the attached map. Treatment is scheduled, and residents in planned treatment areas will be notified regarding the date of treatment prior to actual application.
Cascade will be using ProcellaCOR®, an aquatic herbicide approved by the State Department of Ecology. Cascade has used this herbicide to treat the reservoir since 2019, with good results. It is environmentally friendlier than herbicides used in the past, and results have been significantly better. This treatment may affect water that is used for irrigation, but, as a reminder, pumping or drawing Lake Tapps Reservoir water for irrigation is not permitted.
If property owners plan to remove aquatic plants from the Lake Tapps Reservoir in front of their property, they must follow the rules outlined by the Washington State Department of Fish and Wildlife (WDFW). Additional information can be found here: https://wdfw.wa.gov/licenses/environmental/hpa/types/aquatic-plants. The WDFW rules can be found in the Aquatic Plants & Fish Pamphlet: https://wdfw.wa.gov/publications/01728
In addition, Cascade has teamed up with the Tacoma-Pierce County Health Department to offer residents TappsWise, a natural yard care and septic system maintenance program to keep the Lake Tapps Reservoir clean and healthy. Additional information about TappsWise can be found here: https://www.tpchd.org/healthy-homes/tappswise
For more information, visit https://cascadewater.org/lake-tapps/milfoil/