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Lake Tahoe Aquatic Invasive Plant Control Funded by the Lake Tahoe Science and Lake Improvement Account, SB-630; Implemented by Tahoe Resource Conservation DIstrict

Compiled by Sara Matthews, Tahoe Resource Conservation District (Tahoe RCD). Photographs provided by Monique Rydel, Marine Taxonomic Services & Sara Matthews (Tahoe RCD).

AIS Control at Lake Tahoe

Aquatic invasive species (AIS) in Lake Tahoe threaten water quality, recreation, and aquatic ecosystems. Over the past decade, Tahoe RCD and partners have worked together to prevent, control, and monitor aquatic invasive species at Lake Tahoe. The Lake Tahoe Region Aquatic Invasive Species Management Plan (2014) and Implementation Plan for the Control of Aquatic Invasive Species within Lake Tahoe (Wittman and Chandra 2015) provide the framework for plant control including program goals, and priority species and locations for AIS management. The AIS Action Agenda (2019) re-prioritized treatment sites based on new information and experience gained from implementing AIS control work, establishing new performance metrics to assess success, and identifying the resources needed to carry out a comprehensive, all-taxa approach to addressing AIS in the region.

The Lake Tahoe Aquatic Invasive Species Coordinating Committee (AISCC), co-chaired by TRPA and Tahoe RCD, is a bi-state cooperative that provides direction for addressing AIS issues in the Region, and is comprised of 40 public and private entities and additional stakeholders. Guided by the AIS Action Agenda and the results of the 2018 Lake-wide Aquatic Plant Survey, the AISCC has identified and worked together to fund priority control projects. To date, there are 33 known infestation sites in the Lake Tahoe Region. Half of the infestation sites have been successfully treated and require only annual surveillance visits. Nearly all of the remaining sites are either being actively treated or are being actively planned for future treatment.

Status of known AIS infestations in Lake Tahoe Region

Status of Aquatic Invasive Plant Control Sites, October 2020.

The success of the AIS Control Program relies on treating the Region as a cohesive unit and limiting the spread of AIS populations throughout the lake. This strategy requires a multitude of funding sources. Funding partners have included California Tahoe Conservancy, Elk Point Country Club Homeowners’ Association, League to Save Lake Tahoe, Nevada Division of State Lands, Tahoe Fund, Tahoe Keys Property Owners Association, Tahoe Regional Planning Agency, Truckee River Fund, and more. The contributions of all of these partners ensure that resources are available to address these infestations.

Tahoe RCD – working with a variety of stakeholders

Tahoe RCD is uniquely positioned to implement projects with a variety of partners on the ground – both public and private, to help them meet their conservation goals. Because invasive weeds spread easily through floating fragments, an infestation anywhere can become a threat everywhere. Therefore, cooperation among all stakeholders is needed to successfully tackle this lake-wide problem. Tahoe RCD has successfully used SB-630 funds to facilitate and implement projects around the lake with partners from local municipalities and fulfil the goals of the AIS Action Agenda. From 2016 to 2020, SB-630 funds have funded (partially or fully) ten AIS control projects on the California side of Lake Tahoe. Tahoe RCD has demonstrated success at controlling these satellite populations using a combination of bottom barriers, diver-assisted suction removal, and hand-removal.

Stakeholder designation of SB-630 funded AIS Control Projects

Stakeholder designation of AIS Control Sites funded in part by SB-630 funds

Cooperation from stakeholders around the lake has yielded successful results. The sites discussed below provide an example of some of these partnerships.

Tahoe Vista Boat Launch – Local municipality, North Tahoe Public Utility District

Tahoe Vista Boat Launch is located on the north shore of Lake Tahoe, CA.

In 2016, the drought resulted in low water levels in the lake and Tahoe Vista boat launch became landlocked, creating stagnant water within the marina. A suspicious population of plants was spotted and reported to Tahoe RCD and the League to Save Lake Tahoe.

Low water levels at Tahoe Vista boat launch, 2016.

To ensure that the plants were invasive Eurasian watermilfoil and not a look-alike native milfoil, Tahoe RCD collected specimens and sent them to a lab for genetic analysis. The plants were confirmed to be Eurasian watermilfoil, so Tahoe RCD pursued funding to treat the infestation.

Invasive Eurasian watermilfoil at Tahoe Vista boat launch, 2016.

In 2017, Tahoe RCD contracted with Marine Taxonomic Services to install bottom barriers over the extent of the infestation. Tahoe RCD coordinated with North Tahoe Public Utility District and 27 barriers were installed in early May. The contracted dive team revisited throughout the season to hand remove any invasive plants at the perimeter of the barriers and repair damage from boats. In October, the barriers were removed.

Tahoe Vista boat launch with no invasive plants, 2019.

The barrier treatment at Tahoe Vista was successful. Follow up visits have been carried out from 2018 to 2020 to ensure that no regrowth occurs.

Fleur du Lac Marina– Private Homeowner’s Association

In 2015, a Eurasian watermilfoil infestation was reported at Fleur du Lac Marina. Tahoe RCD worked with the private homeowner’s association to gain access and delineate the infestation.

Fleur du Lac marina is located on the west shore of Lake Tahoe, CA.

The infestation was determined to be Eurasian watermilfoil and the site was assessed for best treatment options.

Diver assessing site and performing hand removal at Fleur du Lac.

In 2016, Tahoe RCD's contracted dive team began control efforts. In 2016 and in 2017, barriers were installed over the densest portions of the infestation, while diver-assisted suction removal and hand-removal were used for other portions of the infestation.

Bottom barriers installed with rebar staples at Fleur du Lac, 2016.
Diver carries out surveillance visit at Fleur du Lac, 2019.

The control efforts were successful. Follow-up surveillance visits from 2018-2020 have shown the return of some native plants, but no regrowth of invasive plants.

Fleur du Lac with no invasive plants, post- treatment 2018.

General Creek outlet - California State Parks

The Eurasian watermilfoil infestation at General Creek was detected during the 2018 Lake-wide Aquatic Plant Survey. Tahoe RCD staff alerted California State Parks of the infestation and worked to plan treatment.

General Creek is located on the west shore of Lake Tahoe, CA.
Eurasian watermilfoil at General Creek, pre-treatment 2018.

Using Early Detection Rapid Response funds, Tahoe RCD's contracted dive team surveyed and mapped the infestation, and hand-removed all visible plants.

Eurasian watermilfoil distribute in General Creek, 2018.

In 2019, the dive-team removed all remaining and reestablished plants from the creek mouth over a series of visits.

Hand removal of Eurasian watermilfoil in General Creek, 2019.
Surveillance visit at General Creek, 2020.

In 2020, several surveillance visits were carried out. Only one invasive plant was found and removed over these visits.

Native vegetation in General Creek, 2020.

Camp Richardson pier – privately-managed marina on US Forest Service, Lake Tahoe Basin Management Unit

The infestation at Camp Richardson was also documented during the 2018 Lake-wide Aquatic Plant Survey. Tahoe RCD coordinated with the US Forest Service – Lake Tahoe Basin Management Unit and with Camp Richardson Marina staff, a private concessionaire.

Camp Richardson pier is located on the south shore of Lake Tahoe, CA.
Eurasian watermilfoil distribution at Camp Richardson, pre-treatment 2019.

During the 2019 season, Tahoe RCD's contracted dive team used hand removal to address the sparsely populated portions of the infestation.

Eurasian watermilfoil distribution at Camp Richardson, pre-treatment 2020.

In 2020, the remaining infestation was resurveyed, and it was determined that diver-assisted suction removal would be the most effective way to treat this infestation.

Eurasian watermilfoil removal at Camp Richardson by day, 2020.

Diver-assisted suction removal is a time-intensive process, but is highly effective at removing all roots and biomass from the system. Tahoe RCD's contracted dive team completed treatment of the entire infestation in August 2020.

Before treatment: July 2020
After treatment: August 2020.

Tahoe RCD intends to continue surveillance visits at this location to ensure that a new infestation is not able to establish.

Funding support from the Lake Tahoe Science and Lake Improvement Account: SB-630

SB-630 funding has contributed to the success of the projects highlighted above as well as several more completed and ongoing AIS control projects. Five out of ten of these projects have been reclassified as surveillance sites, meaning treatment was successful and they require only minimal surveillance to ensure new infestations do not establish.

SB-630 funded AIS Control projects at Lake Tahoe, 2016-2020

It is expected that by 2022, the remaining sites will also require surveillance surveys only.

Maintaining the weed-free state of these project locations will take continued collaboration, dedication, and vigilance. The AIS Action Agenda highlights the need for simultaneously treating established and new infestations with an unprecedented level of effort. One crucial aspect of this plan is the ability to step in quickly to address new or returning infestations before they have the ability to establish and spread further throughout the lake. Tahoe RCD is well-suited to provide the flexible on-the ground expertise for implementing these types of projects, and the availability of funding has been instrumental in providing the capital needed for fast and effective response.

Created By
sara matthews
Appreciate

Credits:

Monique Rydel and Sara Matthews