Indicator
Aquatic Invasive Species Prevention
2023 Evaluation
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Preventing new aquatic invasive species (AIS) from entering Lake Tahoe is one of the broad goals of the Environmental Improvement Program. In 2023 the New Zealand mudsnail was discovered off the South Shore, the first species detected in the Tahoe Basin since the Lake Tahoe Watercraft Inspection Program began in 2008. Under the program, all motorized watercraft are inspected (and cleaned when necessary) prior to launch to prevent the introduction of new AIS. The prevention program also emphasizes preventing the transport of already established aquatic invasive species to other lakes within the Region.

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Status

Watercraft inspections for invasive species and decontaminations prior to launch.

The chart information is sourced from the EIP performance measure Watercraft Inspections for Invasive Species which can be found here: https://www.laketahoeinfo.org/Indicator/Detail/16/Overview#

 

 

2023 Evaluation
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Status
Somewhat Worse Than Target
Trend
Insufficient Data to Determine Trend
Confidence
Moderate
Applicable Standard
WQ8: Prevent the introduction of new aquatic invasive species into the region’s waters.
Key Points
  • All boats are inspected prior to entering Lake Tahoe, to ensure no new species are introduced. Between 2020 and 2023 inspectors decontaminated an average of 3,355 boats annually.
  • Prior to the adoption of the standard and the AIS boat inspection program, 30 non-native aquatic species were already established in the Tahoe Basin's waters.
  • Divers monitoring Lake Tahoe discovered the invasive New Zealand mudsnails in areas off the South Shore in 2023. It was the first time the species had been detected in the Tahoe Basin, and the first new detection of an invasive aquatic species in Lake Tahoe since the threshold standard was adopted in 2012. Lake-wide surveys confirmed that the New Zealand mudsnail infestation was confined to a three-mile area of South Shore.  It is not known when or how New Zealand mudsnails were introduced to the lake. Additional information is available at: https://www.trpa.gov/new-zealand-mudsnail/.
  • Agency response to the discovery of New Zealand mudsnails was informed by a Technical Advisory Committee convened by the Tahoe Science Advisory Council. For additional details see  Preliminary recommendations for Rapid response to the discovery of New Zealand Mudsnail in Lake Tahoe from the committee. Tributatries were sampled in 2023 and 2024 and analyzed for the presence of New Zealand mudsnail DNA and found to be negative.
  • To track the effectiveness of the public awareness campaigns, TRPA tracks the proportion of boats that require decontamination prior to launch. In the prior threshold evaluation period (2016 to 2019), 52 percent of boats required decontamination. That proportion dropped to 45 percent during this current evaluation period (2020 to 2023). A lower proportion of boats requiring decontamination is an indication that boaters are arriving in Tahoe with boats that are cleaned, drained, and dried.  
Evaluation Map
Description

The location of watercraft inspection stations and launch facilities within the Tahoe Region.

About the Threshold
Aquatic Invasive Species (AIS) are non-native organisms that threaten the abundance and diversity of native organisms in Lake Tahoe. Non-native species have been intentionally and unintentionally introduced to the Lake Tahoe Region over the last 150 years. Prior to 1960, a number of species were introduced by managers to augment recreational opportunities. These include a variety of salmonid species including rainbow trout (Oncorhynchus mykiss), Lake trout (Salvelinus namaycush), Kokanee salmon (Oncorhynchus nerka), brook trout (Salvelinus fontinalis), and brown trout (Salmo trutta). The last intentional introduction was of a salmonid prey species, mysid shrimp (Mysis diluviana) in the 1960s. A number of species were likely introduced non-officially by individuals and became established sometime in the mid-1980s and new introductions continued through the first decade of the 20th century. These include warm-water fish species, including bluegill (Lepomis macrochirus), largemouth bass (Micropterus salmoides), aquatic plants Eurasian watermilfoil (Myriophyllum spicatum) and curlyleaf pondweed (Potamogeton crispus), and Asian clams (Corbicula fluminea). The presence of these species continues to threaten native taxa of the lake and is a nuisance to users of the lake. The presence of AIS also results in economic impacts in the Region with potential costs to tourism, property owners, boaters, and maintenance estimated at between $22 to $78 million per year. In December 2012 TRPA adopted the current standard related to the management of AIS in the Region. The presence of aquatic weeds increases nutrients in the system which may impact nearshore clarity.
Non-native species have been both intentionally and unintentionally introduced to Lake Tahoe over the last 150 years. Habitat modification such as channelization and modification of the Truckee Marsh for the Tahoe Keys also created micro-environments within the lake that may be more suitable for colonization by AIS. Climate change further threatens to alter the lake’s physical environment, with the potential for making further AIS establishment more likely.
Delivering and Measuring Success

EIP Indicators

Example EIP Projects

Local and Regional Plans

Monitoring Programs

Rationale Details
Somewhat Worse Than Target. The discovery of New Zealand mudsnail in Lake Tahoe during the evaluation period results in a status determined of non-attainment.
Insufficient Data to Determine Trend. No trend determination was made. The status determination was based on the identification of a single new aquatic invasive species in the Lake, but there is no evidence that this is indicative of a larger trend towards more invasive species in the Lake. Two agency-based monitoring programs (described above) and a citizen science program provide surveillance for new AIS in Lake Tahoe.
Confidence Details
High. New Zealand mudsnail were not known in Lake Tahoe prior to discovery in 2023. Experts and lab DNA analysis confirmed the species is New Zealand mudsnail, an aquatic invasive species (AIS).
Moderate. No trend determination was made because there has only been a single new invasive in the 15 year history of the boat inspection program.
Moderate. If one confidence rating is high and the other is moderate, the overall confidence rating is the lower confidence rating.
Additional Figures and Resources

No photos available.

Preliminary recommendations for Rapid response to the discovery of New Zealand Mudsnail
Uploaded On
7/30/2024
File Type
PDF
Description
Technical Science Advisory Committee Memorandum to Managers on Preliminary recommendations for Rapid response to the discovery of New Zealand Mudsnail in Lake Tahoe | October 2023