Lake Tahoe Aquatic Invasive Species Action Agenda – Emerging Technologies to Play Pivotal Role

Growing problem to be addressed in two phases over a decade

This vessel is equipped with ultraviolet light to attack invasive aquatic plant species in Lake Tahoe - photo: John Paoluccio, Inventive Resources

Emerging technologies will be at the forefront of this summer’s launch of the ten-year, multi-agency effort to address aquatic invasive species (AIS) as laid out in The Lake Tahoe Region Invasive Species Action Agenda

Published in late 2019, Phase I of the Action Agenda aims to aggressively treat and control-test mitigation measures of AIS in the Tahoe Keys from 2021-2025. The environmental assessment and control-testing outcomes from Phase I will then guide the implementation of Phase II’s reduction and eradication measures from 2026-2030.

Aquatic invasive species offer a complex and unique set of challenges for experts looking to find the best mitigation strategy for their Action Agenda.

“There’s no silver bullet, it’s going to have to be this mix and match of initial application and then multiple years of follow up that is both adaptive and variable,” Jesse Patterson, Chief Strategy Officer at the League to Save Lake Tahoe. “It’s better to test as many methods as you can, at first in a controlled way where you can learn and get some new cards in the deck and deal with a better hand when you go after it long-term. That’s the step we’re in now is testing a multi-pronged approach.”

A mat of aquatic invasive species in Lake Tahoe – photo: League to Save Lake Tahoe

In recent years, traditional strategies such as hand-pulling, diver-assisted suction and bottom-barrier mats have been used in select locations with some rates of success against infestations of Eurasian watermilfoil and Curly leaf pondweed. But now, emerging technologies have been tested and their use expanded to complement these previous strategies in hopes of improving their overall effectiveness.

“We strive to be innovative and so we have been piloting a method that uses ultraviolet (UV) light,” Dennis Zabaglo, the Aquatic Resources Program Manager for the Tahoe Regional Planning Agency (TRPA), said. “The first pilot [test] of UV light was back in 2017 on about a half an acre in two different locations. We’ve since expanded that and now are looking to do up to eight acres in 2021.”

John Paoluccio of Inventive Resources in Salida, California, first developed and used the UV light treatment to stop and kill algae growth in caves.

“I developed this system where we went [into the caves] with UV light and that solved their algae problem,” Paoluccio said. “I remember hearing a presentation in Lake Tahoe about finding a solution that will solve this weed problem in the lake. So I met with TRPA and did a little demo on how I can kill aquatic plants using UV light and they gave me my first pilot project at the lake.” 

The first pilot test of UV light in Lake Tahoe was conducted in 2017 on a half an acre in two different locations. They’ve since expanded that and now are looking to treat up to eight acres in 2021 – photo: John Paoluccio, Inventive Resources

Since successfully removing the algae growth from the caves, Paoluccio has also used UV light treatment in ponds and canals. Meanwhile, as the traditional strategies have been effective in satellite locations of infestations like Emerald Bay, the hope is that Paoluccio’s UV light can play a role in the shallow, man-made lagoons that are the primary source of Lake Tahoe’s AIS infestations. 

“Many of the infestations treated successfully were about an acre or less, so relatively small,” Patterson said. “But the Tahoe Keys is 172 acres and over 90% full of these weeds, with boats, piers and five feet of organic muck-layer at the bottom that if you touch turns into a cloud of dust. So the Action Agenda targets sites in the Tahoe Keys because you can’t just address the satellite populations, you have to address that source or you’re never going to get out of this.”

According to Paoluccio, studies in conjunction with the University of Nevada, Reno, so far have shown that UV light treatment is effective on most, if not all types of plants. Although this could pose a risk to sensitive and natural aquatic plants in Lake Tahoe, the advantage to using the UV lights is that it can be switched on and off to target infested areas and work around sensitive areas. 

“With UV light, you simply treat the areas you want the plants to be gone from and leave the other ones standing,” Paoluccio said. “There’s no other technology that can selectively do that except hand-plucking or bottom barriers.”

A typical challenge with the more manual means of treatment like hand-pulling and diver-assisted suction, is that physical removal of plants can kick up sediment that reduces diver-visibility and can unintentionally trigger algal blooms. 

“[Manual methods] can release nutrients that were trapped in the sediment up into the water,” Patterson said. “When you release those nutrients, you can actually trigger hazardous algal blooms that just explode and the water turns green overnight. Since 2017, the Tahoe Keys have had at least one hazardous algal bloom outbreak every year, with a couple years we’ve had multiple and that’s without any disturbance to the bottom.”

UV light is a promising tool in that the invasive plants completely decompose about 14 days after treatment, removing the risks of triggering algal blooms or re-population through plant fragments that can result from manual removal. The key to this strategy, however, is exposing the invasive plants to UV light early enough in the year before the plants develop turians, or seeds, as they mature.

“These plants usually start to drop their seeds in July so if you just get out there in June, they never have a chance to develop the seeds and that really is the key to solving this problem,” Paoluccio said. “Their growth cycle would have to start completely over, new sprouts would grow in and you would treat them again two months later and by then it’s winter and Mother Nature takes care of the rest.”

Paoluccio clarifies that the UV light does not target the roots of the invasive plants, but rather causes such severe damage to the plants’ cells that the plants cannot self-repair. By forcing the root of the plants to restart the growth process all over again, the plant won’t have enough energy to re-establish itself and will die naturally.

“We are affecting the DNA of the plant so that all of their energy is spent trying to repair something that cannot be repaired,” Paoluccio said. “They just fall apart because there’s no more cell structure, no rotting biomass and so it seems like a more natural method of removing these plants.”

While the pilot projects of UV light treatment have shown promising results, Paoluccio assures that it is by no means a one-stop solution. 

“UV works well, but there’s areas where other technologies make more sense and that’s important to understand,” Paoluccio said. “It’s a good tool in combination with other technologies, whether it be hand-plucking, mats and in some cases, herbicides. There’s a lot of areas that are going to be very difficult to solve, so they need to use an array of products.”

A diver deploys a bottom barrier – photo: Tahoe Regional Planning Agency

By understanding which combination of methods will be most effective after years of Phase I testing, a larger-scale implementation of the most effective strategies will begin in Phase II. Currently, the use of two EPA-approved herbicides are being considered on a small-scale testing basis in identified locations of the Tahoe Keys. Their use requires approval from the Lahontan Regional Water Quality Control Board and TRPA, with a decision expected to be made by the end of this year for possible implementation in 2022.

“If herbicides are proposed, they would be used in a one-time treatment in a particular test area and followed up with non-chemical methods like diver-assisted suction, hand-pulling, bottom barriers and even UV light for three years,” Zabaglo said. “From a long-term perspective, seeing what combination of which two methods is going to be the best after three to five years of analyzing will build a large-scale treatment strategy for the whole system.”

Herbicides have never been used in Lake Tahoe due to its classification as a Tier-Three Outstanding National Resource Water under The Clean Water Act, which provides the highest level of protection for a body of water. So although the two herbicides being considered have been used safely and effectively in other locations for decades, Lake Tahoe’s classification complicates their use.

“[This classification] means it’s illegal to degrade the water for any length of time unless it’s a means to an end and there’s no other alternative, which is why herbicides have never been used in Lake Tahoe before,” Patterson said. “The current proposal isn’t actually to apply [herbicides] on any large-scale, but in a very controlled test in the lagoons behind multiple barriers with extensive monitoring and mitigation measures because we need to make sure there are not any unintended consequences.”

The expanded use of UV lights and the ongoing evaluation of herbicides follows the presence of other innovative technologies such as laminar flow aeration and bubble curtains.

“Laminar flow aeration is a fancy way of saying injecting oxygen into the sediment, which sort of kickstarts the organic biology which then eats up the muck-layer,” Patterson said. “The reason that’s important is that the muck-layer is the primary nutrient source for the plants to grow. So you need to remove that muck-layer if you want to prevent these plants from growing back every year.”

Bubble curtains are deployed at the Tahoe Keys development to prevent the spread of invasive aquatic species – photo: Sierra Overhead Analytics

According to Patterson, the bubble curtain resembles a strategy used by whales to trap and feed on fish. The first bubble curtain, which is in the shape of a “V” and pointing into the lagoon, was installed in August of 2018. 

“We thought if it could be used to control fish, you could probably prevent floating plant fragments from spreading, so we designed and installed one at the channel of the Tahoe Keys where it connects to the lake and it’s been hugely successful,” Patterson said. “We’re actually putting a second one in the second channel of the Keys this April.”

The bubble curtains stop the floating plant fragments and corral them to the edges of the channel, where the collected fragments can then be removed. While bubble curtains still allow boats to pass through, they have proven to be a cost-effective measure at catching plant fragments that could be trailing behind them. Despite its seeming early success, Patterson reassures that bubble curtains are not a solution but a mitigation measure that simply buys them more time.

Time, however, is quickly running out as the effects of climate change are already evident in Lake Tahoe’s waters.

“The surface water is far warmer, particularly in the summer months and that’s what the plants need to grow, to thrive and to reproduce,” Patterson said. “These plants are cycling nutrients up into the water column that used to be trapped in the sediments, and algae does really well in warm water with lots of nutrients. The reason why Tahoe is blue is we have very little nutrients, respectively, in very cold water but climate change is warming it really quickly.”

Additionally, a natural occurrence known as “lake-mixing,” is starting to occur less frequently.

“Historically, the lake mixes top to bottom every four years or so, but with the warming of the surface water it’s not mixing as deep every year,” Patterson said. “The lake is now mixing fully every eight years or longer, meaning that it’s not cycling itself. So when it does turn over you’re going to get a big burst of nutrients from the bottom and oxygen from the top all at once and that could trigger massive algae blooms, especially if there’s invasive species altering the nutrient cycle.”

These quickly-developing effects of climate change underscores the importance of controlling aquatic invasive plants at their source in the Tahoe Keys. Therefore, this year’s official launch of the Action Agenda is critical to implementing the best combination of successful measures already used in satellite locations, alongside innovative and emerging technologies on a much larger scale.

“The reason why all these different approaches are being investigated and analyzed is that the Tahoe Keys is 30 times larger than any project we’ve ever accomplished to date,” Zabaglo said. “So looking at every tool that’s possible is warranted because the scale is just so much bigger than what we’ve been able to address so far.”

“We’re going to manage [AIS] to a point of ecological insignificance so that the populations are not altering the ecology of the lake anymore,” Patterson said. “Aquatic invasive species are one of those things that by the time you notice it as a layman, that means we’re losing the battle. So even though the lake looks blue and things seem fine, there’s this war with aquatic invasive species going on that we need to make sure we win.”


Scott King writes about science and the environment for the Ally. Support his work.