The first day of June 1988 was bright and warm, ideal for three young researchers from the University of Windsor who were exploring Lake St. Clair’s bottom. Among them was Sonya Santavy, a newly graduated biologist in a 16-foot boat, as the engine hummed while they navigated toward the lake's center.

On maps, Lake St. Clair appears as a 24-mile-wide bulge in the river system east of Detroit, linking Lake Huron to Lake Erie. It serves as a reservoir for water flowing from Lakes Superior, Michigan, and Huron, which then cascades into Erie and continues toward Niagara Falls, eventually reaching the Atlantic Ocean. The current in Lake St. Clair is so vigorous that a person in an inflatable raft could drift out of it in about two days without paddling.

Water flows swiftly through Lake St. Clair due to its shallow nature, with the exception of a 30-foot-deep navigation channel created by the U.S. Army Corps of Engineers in the late 1950s for ocean-going vessels. Low water levels or high sediment sometimes rendered this channel insufficient, necessitating ships to lighten their loads, often by discharging water from ballast tanks filled with outside water, which could contain diverse organisms collected from ports worldwide.

As Santavy and her team cruised over the rocky lakebed in early summer 1988, she whimsically dipped her sampling scoop into the sediment. Although she was searching for worms, she decided to sample the rocks beneath. To her surprise, she pulled up a scoop of stones, but two of them were unusually stuck together. Upon inspection, she realized one was not a stone; it was alive.

Although the discovery seemed insignificant at the time, following the Seaway’s opening in 1959, non-native species began appearing in unprecedented numbers. The first was the humpbacked peaclam from Europe and Asia, followed by various algae and worms. A water flea from Europe and a European flatworm soon followed, leading to a growing list of invasive organisms infiltrating the Great Lakes ecosystem.

The significance of the zebra mussel lies in viewing it not as an individual organism but as part of a broader ecological threat. Santavy showed her discovery, a living "stone," to a graduate student aboard the boat. They suspected it was a type of clam or mussel, but its unfamiliarity prompted them to bring it back to their lab for further examination.

Upon her return, Santavy presented the specimen to her professors, who were equally puzzled. They sent it to the University of Guelph, where a mussel expert identified it as Dreissena polymorpha, or zebra mussel. This was alarming news. This species, native to the Caspian and Black Sea regions, is notorious for adhering to hard surfaces and forming sharp clusters that can injure swimmers and clog pipes, all while depleting the water of plankton.

Having already invaded waterways throughout Western Europe, the zebra mussel had caused extensive damage. Hungary faced an infestation in 1794, followed by other major cities over the years. When Santavy’s specimen was found in Lake St. Clair, it was approximately 3,000 miles from the nearest known colony.

Although the zebra mussel possesses a "foot" that allows it to move across the lakebed, its movement rate is minimal. Researchers concluded that the mussel likely traveled across the Atlantic in the ballast water of a freighter, as adult mussels cannot survive in saltwater.

Ballast water has historically been used for ship stability, transitioning from solid weights to liquid for ease of loading and unloading. However, this liquid ballast poses significant ecological risks as it often contains living organisms.

The discovery of Santavy's single mussel may have appeared inconsequential, but seasoned ecologists recognized the dire implications. The zebra mussel should be regarded as a malignant presence, akin to cancer cells that spread rapidly in an ecosystem lacking natural predators.

Biologically contaminated ballast water presents an insidious type of pollution because it does not dissipate; it reproduces. A single female zebra mussel can produce up to a million eggs annually, with juvenile mussels able to travel and settle in new locations, perpetuating their invasion.

Despite the alarming news of zebra mussels entering the ecosystem, the academic community had long recognized their invasive potential. As early as the late 19th century, zoologists identified the zebra mussel as a formidable invasive species, capable of thriving in various environments.

In 1981, scientists investigated ballast tanks of overseas freighters bound for the Great Lakes and discovered these tanks teeming with life, including zebra mussels. The U.S. and Canadian governments, however, did not act on this information.

Paul Hebert, director of the laboratory where Santavy worked, voiced frustration over the lack of action against emerging invasive species. The Clean Water Act established that industries required permits to discharge pollutants, but ships were exempted from these requirements, allowing invasive species to flow into the Great Lakes.

Although the Clean Water Act had significant achievements, it inadvertently left a loophole for ships, enabling biological invasions. The introduction of zebra mussels exemplifies the consequences of this oversight, as they proliferated without natural checks on their population.

By the end of 1989, zebra mussels had spread throughout the Great Lakes, reaching areas as far as Chicago and the St. Lawrence River. A concerning development was the discovery of quagga mussels in Lake Erie, closely related to zebra mussels but with even more significant ecological impacts.

Zebra mussels became a costly nuisance for industries, leading to billions in expenses for developing systems to manage their proliferation. However, quagga mussels posed an even greater threat due to their ability to thrive in deeper waters and filter nutrients year-round.

The public often overlooks the scale of ecological changes brought on by invasive species like zebra and quagga mussels. While visible signs of destruction may not be apparent, the underlying transformations are profound, as native fish populations decline and ecosystem structures shift.

The quagga mussel invasion has been so severe that it has altered Lake Michigan’s food web, dramatically reducing plankton levels and impacting fish populations. Surveys indicate a stark decline in prey fish biomass, causing alarm among researchers and fisheries managers.

Invasive species like zebra and quagga mussels have disrupted ecosystems far beyond the Great Lakes, as evidenced by their role in botulism outbreaks affecting bird populations. The cycle of contamination is alarming, creating conditions that lead to widespread ecological consequences.

Despite regulations aimed at ballast water management, invasive species continue to enter the Great Lakes. The challenges posed by ballast water are not limited to the Great Lakes; they extend to other coastal regions worldwide, complicating efforts to control invasive species.

To mitigate the threat of invasive species, some advocate for limiting overseas shipping to protect the Great Lakes, emphasizing the need for enhanced management strategies. Conservationists argue that such measures could prevent the introduction of further harmful species.

Overall, the ecological crisis triggered by invasive mussels underscores the importance of proactive measures to safeguard the integrity of the Great Lakes ecosystem and the broader implications for environmental health.

<i>Dan Egan is a reporter at the Milwaukee Journal Sentinel. He has been a finalist for the Pulitzer Prize and has won multiple journalism awards.</i>

<i>Excerpted from The Death and Life of the Great Lakes by Dan Egan Copyright © 2017 by Dan Egan. With permission of the publisher, W.W. Norton & Company, Inc. All rights reserved.</i>