A fish die-off in Leicester earlier this month has prompted the Vermont Department of Environmental Conservation to investigate whether an insect control group has been over-applying a pesticide meant to control mosquitoes.
The fish kill occurred on the shallow, northern end of Fern Lake, just south of Lake Dunmore on the east side of Leicester. It was reported to the Agency of Natural Resources (ANR) by a resident who reported seeing dozens of dead and dying fish. The ANR’s Department of Fish & Wildlife investigated the kill and concluded it was likely due to a combination of spawning and heat stress.
Meanwhile, the ANR’s Department of Environmental Conservation has begun an investigation into whether there is a link.
The Brandon-Leicester-Salisbury-Goshen Insect Control Group (BLSG), a municipal entity with some state funding, applied pesticides around Fern Lake in late May and early June, around the time when the fish kill occurred.
According to Gary Meffe, the chair of the BLSG, they have been spraying for mosquitoes for more than 20 years and there has never been evidence that the spraying caused a fish kill.
Meffe is a conservation biologist, author of several textbooks on conservation biology and ecosystem management, and editor of a book on live-bearing fishes. He has written more than 80 scientific articles and was the editor of the scientific Journal of Conservation Biology for 12 years.
On May 23 and June 1 BLSG sprayed the roads surrounding Fern Lake. Beginning on May 29, resident Zachary Saxe observed dead and dying fish with black lesions and white puss along the shore. He said the die-off peaked on June 1 and 2, when he found eight species of dead fish: largemouth and smallmouth bass, rock bass, yellow perch, blue gill, pumpkinseed, crappie, and bullhead.
“On Saturday I went for a swim and there were dead fish everywhere and it was every species,” said Saxe. “I was a bit shocked. There was fish still dying. On Sunday I went back out there for a swim and it was still happening. Some of them had these funky looking growths or lesions on them.”
Saxe collected and froze several dozen fish, but left many more that were dead and dying. He continued to find dead fish until June 6, though they were decomposing at that time.
“I’ve seen natural die-offs in Wisconsin where I grew up and they’re usually a single species,” said Saxe, who studied wildlife biology and worked as a wildlife technician in Alaska. He also identified three species of moth and one species of dragonfly that died at the same time as the fish kill.
Around June 1 temperatures soared to the 90s and the weather was sunny, heating up the water in shallow bays. On June 3, Saxe called the BLSG to report the die-off. He says they sprayed down his road the next day. On June 4, Saxe reported the kill to the Fish & Wildlife Department. On June 5, ANR fish biologist Chet MacKenzie surveyed the lake for dead fish and found only one, near the southern end of the lake. He did find numerous spawning beds of panfish and bass in the northern cove and also many live fish, including some of the species that Saxe found. According to MacKenzie, he spoke with two landowners on the south end of the lake who had not seen any dead fish. MacKenzie’s team checked the shore but did not look under debris.
Saxe called MacKenzie the morning of June 6 to tell he him was still finding dead fish.
“At the time I was standing right next to a huge largemouth bass that was all bloated when I called MacKenzie. How can you miss this? They were definitely really decaying and funky, but they were still there,” he said.
Saxe says MacKenzie’s team spent most of their time on the south side of the lake, but that the wind was blowing the fish to the north end. He says no one from the ANR collected any of the fish that he had collected, nor did they take a water sample.
BLSG often uses the pesticide malathion to kill adult mosquitoes. The U.S. Environmental Protection Agency requires agricultural workers to wait six days before harvesting crops from a field that has been sprayed with malathion.
Malathion is an organophosphate pesticide with a garlicky odor and yellowish-brown color. According to the Centers for Disease Control and Prevention, malathion is widely used in agriculture, on golf courses, and in home gardens, as well as to kill fleas and lice on pets and humans. Though acute effects of malathion, which affects the nervous system, on human health are bad — respiratory failure, heart palpitations, vomiting, diarrhea, blurred vision — there is no reliable evidence for chronic health effects on humans. Mammals and birds are better able to break down malathion in their bodies than insects are. Malathion stays in the environment for days to months after it has been applied, though it breaks down quickly in water.
According to the National Pesticide Information Center, malathion is highly toxic to bluegills and largemouth bass. Though malathion has been shown to have dramatic negative effects on aquatic ecosystems, those studies were conducted with malathion concentrations many times greater than the normal application rate.
Saxe is opposed to the pesticide spraying by BLSG. He says when he first moved to Leicester he was taking a walk and got sprayed by a truck. Saxe also asked BLSG to stop spraying his property, where he has an organic garden, and that after three requests they still sprayed, until he put up signs.
Fish & Wildlife attribute kill to heat, stress
MacKenzie, who works for the Fish & Wildlife Department at the ANR, attributes the kill to the combination of fish stressed by spawning and hot, sunny weather. He says small kills like this are common in the spring when the weather changes suddenly and the fish are exhausted by spawning.
The fish kill was enough to lead the Department of Environmental Conservation, a different branch of ANR than MacKenzie’s Fish & Wildlife, to ask whether malathion had anything to do with it. Malathion is the primary ingredient in Fyfanon ULV (ultra low volume), a pesticide that kills adult mosquitoes.
According to Meffe, Fyfanon ULV is sprayed in a swath 150 feet on either side of the road. The truck that applied the pesticide drives at 5 to 7 miles per hour and only does one pass. The spray nozzles were calibrated in mid-May, which ensures that the right amount of pesticide is released. The pesticide is applied at night so that it doesn’t affect bees and butterflies, no more than once every four or five days, and sometimes months go by between applications. Spraying occurs as needed — often, residents call the BLSG and ask that their neighborhood be sprayed. The bay where the dead fish were found does not have a road running adjacent to it, though roads that were sprayed are as close as 1,000 feet.
“In a perfect world we wouldn’t ever have to do this, obviously. Nobody ever likes to apply pesticides,” said Meffe. “In a nearly perfect world we would only have to use larvicides, which are very focused on mosquitoes with almost no other mortality. Of course, the world is much more complex than that and we have adults emerge. In past years these were only nuisance mosquitoes, but even nuisance mosquitoes affect people, affect the economy, affect business. In recent years we have had West Nile virus and Eastern equine encephalitis. We had two people die in the Brandon area in the last year from EEE. We certainly follow every precaution, every control, every prescription to apply pesticides properly, no more than we need to, and the least that we can get away with because it’s expensive.”
Meffe is disappointed there is no actual evidence as to whether the spraying caused the kill or not. “Without a water sample you can’t say no, there was no pesticide in the water, but neither can you say yes,” said Meffe. “If it was us I’d sure want to know, and I wish someone had taken samples because then we could address it.”
The BLSG is funded largely by tax money from the four participating towns. That money pays for general costs and the pesticides to kill adult mosquitoes. The state agency of agriculture supports the BLSG with a grant for aerial spraying of larvicide. The group is regulated and permitted by the state.
Meffe makes it clear that he doesn’t know whether the pesticide caused the fish kill or not. It could have been the combination of spawning stress, heat and pesticide. “There could have been parasites, bacterial disease, there could have been people splashing around in the water that increased stress. I mean, you just don’t know. There’s all sorts of stressors that fish are subject to.”
Eric Palmer is the director of fisheries at the Fish & Wildlife department. In an email to coworkers before MacKenzie surveyed the lake, Palmer wrote, “It sounds like Mr. Sacks [sic] knows Fern Lake well, and this fish kill is not a ‘normal’ occurrence on the lake. The report of multiple species of fish being killed raises some concerns as many fish kills are limited to one or two species that have been stressed by normal activities like spawning. The reports of dead dragonflies … and moths … could just be coincidental, or may suggest an even broader cause of mortality.”
Palmer’s email went on to say, “One challenge for us is to separate causation from correlation. For example, fish could be stressed by one factor (such as a manure spill, chlorine spill, high temperature event, etc.) and as they are dying and their immune system is compromised they may get infected by a common bacteria (such as columnaris). If we investigate after the fact we may only be able to detect the columnaris. Once fish are dead, their bodies are quickly colonized by a host of other bacteria and it becomes very difficult to draw any conclusions.”
Palmer suggested that his team look at whether they could find disease in the dying fish and whether there are any identifiable stressors. But, he laments, “The suggestion by Mr. Sacks [sic] that mosquito spraying may be a possible cause of the mortality is something that our Department is not well equipped to investigate. We do not have any equipment to test for the presence of pesticides, and would only be able to look for a pattern (i.e., have there been any other multi-species fish kills in proximity to mosquito spraying) which would again just be correlation and not necessarily cause-and-effect.”
Rick Levey, an aquatic biologist with the Department of Environmental Conservation, wrote in an internal email that, “I agree that the Fish Kill may have been caused by rising water temperatures and spawning stress, but I also feel it prudent and necessary to further investigate potential non-target impacts from frequent use of Malathion adjacent to these surface waters.”
According to Levey, Fyfanon ULV has a high potential to drift long distances through the air and soil. Levey estimates that the half-life of malathion is one week in Fern Lake, based on the pH. This means that the malathion from the spraying on May 23 was nearly half gone by the time Saxe began to see dying fish on May 28. Levey wrote in his internal email calculating the possible effects of the spraying that malathion is “highly to very highly toxic” to aquatic life. According to his calculations, the application of malathion could have exceeded the EPA’s safe limit for aquatic life by almost 500 times. Levey makes several assumptions about the concentration of malathion in the water, including how much, if any, actually made it from the spray truck to the lake; he assumed 10 percent for five minutes and based all of his calculations off that amount.
Saxe says that last night he stood next to the water while the trucks were spraying and the mist of pesticide made his eyes burn.
Whether the Fern Lake fish kill was caused by malathion or not, the result is an investigation into the effects of pesticide spraying on aquatic life. Levey wrote in his email that the Department of Environmental Conservation will be working with the agency of agriculture and the BLSG to review application methods as well as pesticide concentrations and ecological effects in nearby water bodies.
