EarthTec QZ treatment part of Colorado Parks and Wildlife zebra mussel eradication plan for Highline Lake

by Jan 30, 2023

Colorado Parks and Wildlife will use EarthTec QZ to contain and eradicate zebra mussels from Highline Lake.

Loma, CO. – Colorado Parks and Wildlife (CPW) has approved a plan to eradicate zebra mussels from Highline Lake in Highline Lake State Park. The invasive mussels, native to the Black and Caspian Seas, were first discovered in Highline Lake by researchers during a routine invasive species sampling in September 2022. Additional adult mussels were found in October.

This is the first time the invasive species has been detected in Colorado waters, prompting the CPW to change the status of Highline Lake from “suspected” to “infected.” Once established, zebra mussels can produce at an alarming rate. A single female can produce up to a million eggs in a season. If left unchecked, zebra mussel colonies can cause disastrous impacts, from smothering native mollusks to fouling infrastructure.

“The next phase to remove zebra mussels from the lake will be twofold,” said Highline State Park manager Alan Martinez. “Our goal is to eliminate the mussels while protecting a quality warm water fishery that has taken decades to build.”

The first step in eradication is to lower the lake by approximately 30 feet. The lake was previously lowered 10 feet to allow researchers to inspect an inlet pump for the presence of zebra mussels in November 2022. Lowering the water level will expose the mussels near the shoreline, causing them to die from desiccation and freezing temperatures.

Around March, researchers will apply EarthTec QZ, an EPA-regulated molluscicide, to the east side of the lake. Two weeks later, it will be applied to the west side. This approach will allow fish and other aquatic species to move to parts of the lake where chemical concentrations are lower.

Following the treatment, the water will be tested weekly for the presence of zebra mussels. Even if none are found, the lake will be considered “infested” for the next five years. During this time, boats must undergo a mandatory inspection before leaving the park.

“We are optimistic that with the combination of lowering Highline Lake and EarthTec QZ application, we will be able to eradicate the mussels while limiting impacts to non-target organisms including preservation of the warm water fishery that Northwest Region staff have worked so hard to build.” said Walters.

Earth Science Laboratories Inc. develops and manufactures sustainable chemical water treatment products for use in municipal, agricultural, and recreational waters. EarthTec QZ is an EPA-registered molluscicide used to control zebra and quagga mussels in pipelines and open waters. It is NSF certified to Standard 60 as an additive to drinking water. More information is available at


Colorado Parks and Wildlife. 2023, January 26. CPW to begin zebra mussel mitigation treatment at Highline Lake [Press release].