Aquatic Invasive Species

Over the past 130 years, numerous nonnative fish, invertebrate, and plant species have been introduced — both intentionally and unintentionally — into Lake Tahoe, altering its ecology and food web.

The earliest wave of introductions occurred between the late 1800s and the 1940s, when fish such as rainbow trout, brown trout, lake trout, brook trout, and kokanee salmon were stocked to support recreational fisheries. Other species, including crayfish and Mysid shrimp, were intentionally introduced to enhance food sources for game fish.

More recent introductions have been accidental or illegal. Largemouth bass and bluegill were unlawfully introduced and have established populations in parts of the lake. Aquatic plants such as Eurasian watermilfoil and curlyleaf pondweed first became established in the Tahoe Keys and have since spread to other nearshore areas. The Asian clam, discovered in 2002, now forms dense beds in the southeastern portion of the lake — reaching densities of approximately 1,500 clams per square meter.

Each introduction, whether deliberate or inadvertent, has had measurable impacts on native species, water quality, and ecosystem processes.

New Zealand Mudsnails: A Recent Wake-Up Call

In September 2023, New Zealand mudsnails were detected in South Lake Tahoe, marking a significant new threat to the Basin. These tiny, highly invasive snails reproduce rapidly and can disrupt food webs by outcompeting native invertebrates. They are easily transported in small amounts of water or mud, making them particularly difficult to control once established.

The discovery intensified regional prevention efforts. It strengthened the Lake Tahoe boat inspection program and placed new emphasis on outreach to both residents and visitors about the risks of unknowingly transporting aquatic invasive species — especially via non-motorized watercraft such as kayaks, paddleboards, and inflatables. Because these vessels often move between water bodies without inspection, they can become pathways for the spread of invasive species if not properly cleaned, drained, and dried.

Research, Monitoring, and Prevention

In collaboration with researchers at UC Davis main campus, TERC continues its long history of studying the population dynamics and ecological impacts of introduced species in Lake Tahoe. TERC is now expanding its invasive species research by bringing environmental DNA (eDNA) technology to Lake Tahoe. eDNA sampling involves collecting water samples and analyzing them for traces of DNA shed by organisms. By screening for the genetic signatures of known invasive species, researchers can detect their presence even at very low abundance — often before populations become visible or widespread.

This work aims to demonstrate that eDNA is a viable, accurate, and cost-effective tool for early detection. Rapid identification of new invasive species could enable agencies to implement response and containment strategies quickly, increasing the likelihood of limiting their spread and protecting Lake Tahoe’s ecosystem.

Preventing new introductions remains the most effective and least costly strategy. The detection of New Zealand mudsnails serves as a powerful reminder that protecting Lake Tahoe requires vigilance, research, and shared responsibility from everyone who uses and enjoys the lake.

You can learn more about how you can protect Lake Tahoe and other water bodies from aquatic invasive species from the resources below:

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Interactive Aquatic Invasive Species Exhibit

Become a Tahoe Keeper