In 1988, cargo ships accidentally brought zebra mussels to the US in their ballast water, and they devastated the Great Lakes, but a 2026 study finds that after 20 years in Kansas lakes, they barely changed the fish or the water

In June 1988, a biologist sampling Lake St. Clair pulled up something no one recognized: a striped, thumbnail-sized mollusk clinging to a rock. According to the U.S. Geological Survey article, 'Distribution and dispersal of the zebra mussel (Dreissena polymorpha) in the Great Lakes region,' the species likely hitched a ride from Europe in the ballast water of a transoceanic cargo ship, which dumped its tanks into Lake St. Clair sometime around 1986. That chance discovery turned into one of the most consequential invasions in American freshwater history.

Zebra mussels spread quickly, and the damage came after. According to a 2007 study, 'Economic Impacts of Zebra Mussels on Drinking Water Treatment and Electric Power Generation Facilities in Environmental Management' by Nancy A. Connelly et al. , published in the journal Environmental Management, the mussels have cost North American power plants and drinking water facilities an estimated $267 million between 1989 and 2004, mostly from clogged intake pipes.

The species changed more than infrastructure; it reshaped entire lake ecosystems by filtering out massive amounts of phytoplankton and nutrients, a process associated with crashes in native fish food sources throughout the Great Lakes and the Hudson River.


So when zebra mussels began appearing in lakes all across Kansas about two decades ago, fisheries scientists figured they would see a repeat performance. A new study says it largely didn’t.

Nobody was planning a 20-year experiment
A new study titled 'Two decades of zebra mussel (Dreissena polymorpha) invasion in Kansas reservoirs have minimal effects on water quality and fish communities,' published in Frontiers in Environmental Science by Ridge Sliger et al. , by researchers at Kansas State University and the Kansas Department of Wildlife, Parks and Tourism shows zebra mussel invasions in 25 large Kansas reservoirs have had almost no measurable effect on water quality, fish populations or angler activity in the past 20 years.

The researchers had a uniquely comprehensive data set to work with. They accessed water quality records from 1975, fish abundance surveys from 2010 to 2024, and angler creel data from 1999 to 2025, across reservoirs from El Dorado, the first invaded in 2003, to Tuttle Creek, invaded in 2017.

They looked at four water quality parameters known to be affected by zebra mussels through filter feeding: water clarity, total phosphorus, total nitrogen, and chlorophyll levels. They used machine learning models to see whether years since invasion predicted any changes in these, and compared this with other factors such as which specific reservoir was being measured and the calendar year.

The water barely reacted
The study found that in every single model, the strongest predictor of water quality was reservoir identity, basically which lake it was. Overall, zebra mussel detection was a poor predictor, trailing behind reservoir identity and, at times, even the calendar year itself. The same pattern held for clarity, phosphorus, nitrogen, and chlorophyll, offering little evidence that the mussels were filtering at a scale that would meaningfully influence the chemistry of these reservoirs.

Fish numbers barely moved either
The team then compared population trends for 19 fish species, including largemouth bass, bluegill, walleye and channel catfish, between invaded and uninvaded reservoirs. Results from the study revealed no statistically significant difference in abundance trends associated with invasion for 18 of those 19 species.

The only exception was largemouth bass, which declined slightly in invaded reservoirs. But the size of that decline, at most a handful of fish out of typical sample totals, was unlikely to be biologically meaningful for the fishery, according to the researchers.

Angler behavior followed the same pattern. Creel survey analyses from the study found no difference in the mean number of anglers observed at boat ramps and shorelines between invaded and uninvaded reservoirs, and no change over time coincident with the arrival of mussels.

Why Kansas reservoirs might be getting off easy
The likely reason comes down to habitat. The study, 'Low densities and little change in water clarity characterize zebra mussel invasions near the southern extent of their range,' published in Biological Invasions by Jacob A. Cianci-Gaskill et al. , reservoirs are generally warmer, murkier and more variable in water level than the natural lakes on which zebra mussels tend to thrive, conditions that seem to limit how dense the mussels can become and how much filtering pressure they can exert.

Kansas is on the western edge of the species’ current U.S. range, so its reservoirs may just never reach Great Lakes-style mussel densities. In this case, lower density seems to equate to lower disruption.

Not a green light to stop worrying
None of this completely clears up zebra mussels. But whatever they do to fish, they remain an expensive infrastructure problem. And the Kansas researchers aren’t anywhere near saying the threat is gone. Uninvaded reservoirs in the study were generally smaller than invaded ones, they note, suggesting that habitat quality may not be the main factor determining which lakes are invaded first, and that boating traffic is the primary driver. This means that most Kansas waterbodies are still vulnerable to invasion, no matter how mussel-friendly their habitat looks.

For the moment, at least, anglers casting lines into Kansas reservoirs can take some solace. The fish in these reservoirs are still biting; the water has remained steady, and twenty years after this invader arrived in American waters and changed the Great Lakes, one of the country's most notorious aquatic invaders has, here at least, pretty much kept to itself.