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A significant majority of Missisquoi River’s male smallmouth bass bear eggs, a characteristic known as “intersex.”

Researchers believe the condition results from agricultural runoff in the Missisquoi River watershed, an area where farmers already face scrutiny for phosphorus pollution that promotes blue-green algae blooms in Lake Champlain.

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A report published this fall, the most comprehensive of its kind, found 60 percent to 75 percent of male smallmouth bass in the Missisquoi River carry eggs.

Agency of Agriculture officials say the report does not establish farming as the cause of the dual sex traits in fish, and say that Vermont’s piscene population actually showed less incidence of androgyny than those of other states in the study.

Clean-water advocates have called on legislators and state agencies to take action in response.

“The alarm to me is that these chemicals are present — they’re in our water, they’re in our food, we’re exposing ourselves to them — to me, that’s the alarm,” said Vicki Blazer, fish biology researcher for the U.S. Geological Survey, and one of the report’s authors. “Obviously, humans are not going to be exposed in the same way fish are: We’re not constantly in the water, our drinking water is treated, but that doesn’t mean we’re not exposing ourselves to many of the same chemicals. To me, that’s the concern.”

Blazer identified several potential causes of Missisquoi River’s intersex fish, all of them resulting from agricultural practices.

James Ehlers, executive director of Lake Champlain International, said the abnormal sexual development of the small bass is “horrific.”

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“I think they’re basically Franken-fish. It’s a canary in a coal mine, except it’s a bass in a river, and there’s something monstrously out of balance in the natural system.”

The intersex fish likely result from one or a combination of three substances, Blazer said.

An herbicide called atrazine is one possible cause, she said. Previous studies have shown that atrazine can trigger certain animals to develop traits of both sexes, she said.

Atrazine is the pesticide most commonly found in drinking water in the United States, and in 2012 a court case forced its manufacturer to pay over $100 million to filter the herbicide from a number of drinking water sources.

The European Union has banned the chemical’s use.

Confined animal feeding operations could also cause Missisquoi Bay’s bass to develop characteristics of both sexes, Blazer said.

Sometimes called “factory farms,” these facilities contain within relatively small spaces large numbers of animals for the purpose of cheaply producing meat and other animal products.

All animals naturally excrete hormones, Blazer said, and this type of farm produces especially high quantities of animal excretions.

Farms can also generate what are known as phytoestrogens, Blazer said. These molecules originate in plants and mimic estrogens produced by animals. Agriculture operations permit this substance to develop in sufficient concentrations to be thought to affect fish biology, Blazer said.

The cause of Missisquoi Bay’s egg-bearing male fish is probably one or all three of these, she said.

“The big thing to me is that we don’t truly understand the mix of things fish and other organisms are exposed to,” she said.

Agency of Agriculture representatives say they don’t intend to revise current practices in light of the study’s findings.

“The data in the study are in no way indicative of a need for regulatory change on herbicide applications in Vermont,” said Cary Giguere, Agrichemical Program Manager at the Agency of Agriculture. “We have no idea of the [intersex-causing pollutant] source. In some ways, the study shows proper management and protection.”

Giguere said that the study showed intersex fish even in waters where no agricultural or other pollutants could have entered the waters. Giguere also said that Vermont showed the lowest incidence of intersex fish of any state in the study. The study covered rivers in 10 northeastern states.

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Vermont did have the lowest rate of intersex fish in the study, but 60 percent is nevertheless a worrying level of egg-bearing males in a fish species, said the study’s lead author, Luke Iwanowicz.

Even in the Chesapeake Bay watershed, fish are found with as low as a 10 percent rate of egg-bearing males, Iwanowicz said.

Egg-bearing male smallmouth bass at any level should be considered unnatural and indicative of harm to the species, Blazer said.

Although the study found intersex fish in waters unaffected by agriculture, a strong correlation exists between the intensity of agricultural practices and the prevalence and severity of intersex fish, Iwanowicz said.

“We always get in trouble if we try to say, ‘it’s only this, or only that,’” Iwanowicz said, “but with smallmouth bass especially, we’re very consistently finding [egg-bearing males] associated with agriculture.”

Iwanowicz said a compound found in the mouths of fish at higher concentrations in Missisquoi River than any other in the study might offer further evidence of this association.

Vitellogenin is a substance that indicates recent exposure to the estrogens that cause intersex fish, he said. Intersexuality is a trait caused by exposure to abnormal estrogen levels early in life, he said. That Missisquoi River fish have the lowest intersex rates but the highest vitellogenin frequency suggests that the source of intersex-causing estrogens is likely periodic, rather than constant.

This points toward a source like farm runoff, occurring during rain events, as opposed to the steady flow of effluent produced by sources like wastewater treatment plants, he said.

Farms in the Missisquoi Bay watershed have already been implicated as a source of the phosphorus that causes blue-green algae blooms in the bay, and Blazer said she hopes high-profile pollutants such as phosphorus don’t lead scientists, regulators and water users to overlook other pollutants such as those altering piscene sex traits.

Blazer said the phenomenon of intersex fish is assuredly a product of human activity.

Ehlers said he’s bent the ear of several legislators, some of whom have promised to consider the matter before the state’s lawmaking body.

House members have been made aware of the issue, and are currently scheduling hearings on the matter, Speaker Shap Smith’s chief of staff Dylan Giambatista said.

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