Aquatic Invasive Weed Control and Costs

The developer of the Tahoe Keys, and subsequently the Tahoe Keys Property Owners Association (TKPOA), have been working to control aquatic weeds in the lagoons since the 1970s. Seasonal harvesting has been the main weed control practice since the mid-1980s, removing more than 10,000 cubic yards annually at a cost up to $400,000 per year.

Beginning in 2001, TKPOA increased their efforts to control the aquatic weeds by:

  • Researching control methods
  • Experimenting with bottom barriers
  • Collaborating with TRPA and the Tahoe Resource Conservation District
  • Consulting with the Lahontan Regional Water Quality Control Board, Lake Tahoe Aquatic Invasive Species Coordinating Committee and others
  • Conducting extensive scientific monitoring that has resulted in more than 20 scientific reports dating back to 2004

TKPOA has spent $3,700,000 to date on AIS and water quality issues, and anticipates spending $2,000,000 more by 2020. Tahoe Keys property owners are feeling the heavy burden of this onerous issue.

CURRENT TKPOA CONTROL METHODS

Mechanical Harvesting & Fragment Collection

To date, this has been the main method of weed control in the Tahoe Keys – and it hasn’t been successful. Harvesting entails using large watercraft to mow the tops of aquatic weeds so boats can pass through the lagoons. The Tahoe Keys Property Owners Association has spent up to $400,000 a year on this method, only to see weeds increase in volume due to the spread of fragments. With new technology and methodologies, the association aims to reduce harvesting and the associated spread of fragments and new infestations. In 2017, TKPOA staff removed 9,996 cubic yards (that’s more than 900 dump trucks) of aquatic weeds from its lagoons, an undertaking that totaled more than 6,000 man-hours of work.

a metal grate filtering weeds out of the water
a close up of milfoil in a dumpster
a trailer full of weeds

Bottom Barriers

men pulling tarps out of the water on a lake

Bottom barriers, mats designed to smother aquatic weeds, are currently in use in the Tahoe Keys lagoons. TKPOA is allowed a total of five acres of bottom barrier coverage (Tahoe Keys lagoons are 172 acres in water-covered area). While effective for small areas, they kill all plants, not just invasive weeds. Bottom barriers are useful for relatively small scale infestations and for individual property owners around their docks. In 2017, TKPOA placed the largest bottom barrier coverage to date.

Article: Momentum picks up in fight against invasive plants in Tahoe Keys

Tahoe Daily Tribune, July 2017

Cultural Controls and Non-Point Source (NPS) Plan

Working with property owners to reduce nutrients from excess fertilizer and other contaminants flowing into Lake Tahoe that encourage weed growth.

an illustration of a home with a dock and channel

As part of the Waste Discharge Requirements (WDRs) issued to TKPOA by the Lahontan Regional Water Quality Control Board (Lahontan Water Board), TKPOA has prohibited the use of phosphorus-containing fertilizers, encouraged the reduction of lawn irrigation, and conducted “lunch and learn” seminars for contractors to educate them on ways to reduce the release of nutrients and other contaminants (e.g. from construction work, landscaping or from draining spas) into Tahoe Keys lagoons.

By working with property owners to reduce runoff and use of fertilizers on land, less nutrients will be introduced into the water that may contribute to weed growth. The Lake and Lagoon Friendly Landscaping Campaign, launched in 2016, aims to minimize these nutrients while also generally improving water quality.

Boat Backup Station

TKPOA created a boat backup station and associated educational materials to reduce the spread of fragments that can create new infestations around the lake. First implemented in the spring of 2016, TKPOA’s boat backup station is designed to reduce aquatic invasive weed fragments being carried out of the Tahoe Keys into greater Lake Tahoe by boat propellers.

Controlling these fragments is key – as Eurasian watermilfoil and curly leaf pondweed can propagate from fragments. Observed increases in curlyleaf pondweed, which is able to grow at greater depths, makes this more urgent.

https://www.keysweedsmanagement.org/blog/boat-backup-station-makes-progress-in-2017

Bubble Curtain

boat driving through channel

photo credits: League to Save Lake Tahoe

bubbles in the water

Installed and partially funded by The League to Save Lake Tahoe to minimize the spread of weed fragments into Lake Tahoe, the bubble curtain creates a barrier of bubbles in the water column across the west channel between the Tahoe Keys lagoons and Lake Tahoe.  Used in other locations around the world (including places with currents, tides and swells) to prevent debris from moving through an area—this is the first time this technology has been used to prevent the spread of aquatic invasive weeds.

TKPOA purchased two Sea Bins—autonomous devices designed in Australia to collect debris in the water—that will be placed on either end of the bubble curtain to capture and remove fragments as they are corralled.  The Sea Bins are expected to be installed in Spring 2019.

The bubble curtain, together with the boat back-up station, is designed to significantly reduce the number of weed fragments that leave the Tahoe Keys lagoons and enter Lake Tahoe.

http://www.ktvn.com/story/38301051/bubble-wall-could-stop-spread-of-aquatic-invasive-plants-in-lake-tahoe

https://www.tahoedailytribune.com/news/bubble-curtain-to-contain-invasive-plants-in-tahoe-keys/

https://www.keeptahoeblue.org/news/tahoe-in-the-news/Bubble-Wall-Could-Stop-Spread-of-Aquatic-Invasive-Plants-in-LakeTahoe

https://www.keysweedsmanagement.org/blog/tahoe-keys-testing-new-technology-to-combat-spread-of-weeds

https://www.keeptahoeblue.org/our-work/ais/Tackling-aquatic-invasive-plants-in-the-Tahoe-Keys

Laminar Flow Aeration

TKPOA applied for permits from various regulatory agencies in 2018 to test a technology called Laminar Flow Aeration (LFA). LFA involves bubbling air through several diffusers on the bottom of the lagoons. The air bubbles cause the water to circulate, increasing the amount of oxygen at the bottom of the lagoons, which in turn changes the form of some of the nutrients in the sediment and “muck”. This change is intended to make the nutrients less available for the weeds, which should reduce the rate and amount of weed growth in the area of the LFA test. The test will be conducted in the lagoons adjacent to Christie Drive, north of Venice Drive. TKPOA has received financial support for this project from The League to Save Lake Tahoe, who will be monitoring the project and gathering data throughout a three-year pilot project to learn if this technology can be effectively applied to other infested areas at Lake Tahoe.

Having acquired permits and regulatory approvals in late 2018 and early 2019 from the Tahoe Regional Planning Agency (TRPA), the California Department of Fish and Wildlife, the U.S. Army Corps of Engineers, and Lahontan Regional Water Quality Control Board, TKPOA has installed the LFA system to assist with long term water quality management. The number of regulatory approvals needed for this simple test illustrates some of the challenges that TKPOA faces in finding and implementing solutions to the aquatic invasive weed infestation. A similar test was recently approved and installed at Ski Run Marina.

https://www.keeptahoeblue.org/our-work/ais/Tackling-aquatic-invasive-plants-in-the-Tahoe-Keys

Potential Studies Pending on Funding and Permitting

  • Floating Wetlands
  • Ultraviolet (UV) Light Study
  • Reviving elements of the Tahoe Keys Lagoons water circulation and treatment system
  • EcoSOAR ionization system
  • Electronic Data Collection Systems

For extensive information on TKPOA Weeds Management visit https://www.keysweedsmanagement.org