Utah Lake carp removal
Carp in a net in Utah Lake. The fish, introduced to the lake in the late 19th century, are now being removed from the lake to help preserve native species. Credit: Chad Landress, CC BY 2.0

A new study of a shrinking lake in Utah has found elevated levels of polychlorinated biphenyls, or PCBs, in species of fish that are often caught for sport and consumption. The preliminary results suggest that an effort to rid the lake of an invasive species is not yet achieving an ancillary and hoped-for benefit of reducing chemical contamination.

PCBs do not occur in nature. Industry made wide use of these chemicals up until 1979, when they were banned by the U.S. Environmental Protection Agency (EPA) because they had been found to be toxic and a probable human carcinogen.

“Even though these chemicals are banned, they are still landing in the lake.”

But “even though these chemicals are banned, they are still landing in the lake,” said Victor Sanjinez-Guzmán, who did the research as an undergraduate student at Utah Valley University in Orem. He presented his research on behalf of a team led by associate professor Eddy Cadet last week at the American Geophysical Union’s 2017 Fall Meeting in New Orleans, La.

The study site, Utah Lake, has ancient origins. Like the Great Salt Lake, it is a remnant of Lake Bonneville, which once covered 51,000 square kilometers (20,000 square miles) to as deep as 300 meters (1,000 feet). Now Utah Lake is a shallow body of freshwater near the Utah cities of Provo and Orem. A popular lake for recreation and fishing, over thousands of years it has diminished to an area of 383 square kilometers (148 square miles) and an average depth of 3 meters (10 feet). The source of the PCB contamination in the water is unknown and likely is not from a single point source, said Sanjinez-Guzmán.

Fishing in Troubled Waters

People introduced carp into the lake in the late 19th century for human consumption. Since then, the invasive species has damaged vegetation needed by an endemic fish—the critically endangered June sucker (Chasmistes liorus). The June Sucker Recovery Implementation Program, a state and federally funded coalition, is now systematically removing carp to save this native species. They hope to reduce the carp population by at least 75% to promote a more balanced fish community, improving the overall health of the ecosystem.

The team hypothesized that removing the carp from the lake would result in removal of some PCBs from the system.

Now enter PCBs. The chemicals are not water soluble, so they often reside in sediments where the carp feed.

“The carp have relatively high levels of PCBs, and the carp are also a sink for the PCBs,” explained Cadet. So the team hypothesized that removing the carp from the lake would result in removal of some PCBs from the system. And if some PCBs are removed from the system, they’re also less available to the lake’s other fish.

Carp “are trash fish compared to prize stock fish, but people still eat them, and we don’t really study it,” said Jim Gawel, an associate professor from the University of Washington Tacoma who was not involved with this study but conducts similar research in Washington State.

Cadet also noted that even if people who fish in the lake don’t eat carp, they use it as bait for other fish. This is a concern because PCBs can be magnified in larger fish—as other species consume PCB-laden prey, the chemicals get incorporated into their bodies; as those species in turn get eaten, the chemicals move up the food chain and possibly to our dinner plates.

Deciphering Trends

The research team analyzed five species of fish, including carp (Cyprinus carpio), channel catfish (Ictalurus punctatus), and walleye (Sander vitreus). By weight, the carp make up the largest share of the lake’s biomass.

Of the 125 individual fish sampled, some of them had higher levels of PCBs in their flesh and organs than had been measured in a previous study in the lake in 2008. “For fillet tissues, walleye, common carp, and channel catfish were higher than the initial 2008 study. PCB was non-detectable in both white bass and black bullhead fish. This means that the PCB concentration declined for these fish,” says Cadet.

For carp in particular, fish classified as “small,” “medium,” and “large” were caught. The largest fish had the highest level of PCBs in their tissues: Those fish have lived longer and thus have fed in more PCB-laden sediments.

Results point to the idea that the carp removal program might not yet be decreasing the levels of PCBs found in all sport fish.

But what about the higher overall levels compared to the 2008 study? “This seems to indicate that the PCBs are likely magnified in the tissues of the larger fishes,” said Cadet. Those fish eat smaller fish, so such biomagnification is expected, he explained.

Results are preliminary but point to the idea that the carp removal program might not yet be decreasing the levels of PCBs found in all sport fish. Further detailed study is needed to better understand what the larger trend will be over time.

Hidden Danger?

Fish consumption advisories for Utah Lake have previously been issued because of PCB contamination. In 2006, the Utah Department of Health issued a consumption advisory regarding the lake’s carp because the levels of PCBs exceeded EPA standards. In 2007, the consumption advisory was extended to include channel catfish because they also contained elevated levels of PCBs.

However, U.S. Food and Drug Administration (FDA) standards for PCBs in fish are less strict than EPA standards and allow a tolerance level of 2 parts per million in fish. None of the fish in this study had PCB concentrations that high, except for walleye, Cadet explained.

“People around the lake eat a lot of the fish. I tried the walleye, and it was delicious,” Sanjinez-Guzmán joked, noting he ate it before he saw the results of his team’s study.

The researchers stressed that the effect of removing carp from the system may take time to be seen in other fish, if it’s seen at all.

Nonetheless, Cadet remains hopeful. If the removal of the carp not only helps increase the lake’s clarity and the recovery of the June sucker but also decreases biomagnification of PCB levels in fish, then everyone wins, he noted. That potential “is good news for anglers who consume the fish from the lake.”

—Shaena Montanari (email: shae.montanari@gmail.com; @DrShaena), Freelance Science Journalist

Correction, 9 January 2018: A prior version of this story did not fully capture the nuanced results of the research’s preliminary findings. The current article provides this nuance.


Montanari, S. (2017), Modern chemicals from mystery source taint fish in Utah Lake, Eos, 98, https://doi.org/10.1029/2017EO089393. Published on 21 December 2017.

Text © 2017. The authors. CC BY-NC-ND 3.0
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