Zebra mussels, which originally come from the Black Sea and Caspian Sea, were accidentally introduced to North America in the early 1980s. They made their way into the Great Lakes in 1988, likely through ballast water discharged by large ships that travel across oceans. A biologist named Jim Carlton had predicted this method of introduction in a study from 1985. Although concerns were raised about the risk of invasive species, it took until 1990 for the United States to start regulating ballast water. However, ships that claimed they had no pumpable ballast water were not required to empty their tanks, allowing zebra mussels and other organisms to continue spreading. It wasn’t until 2006 that the U.S. and Canada required ships to rinse their ballast tanks after extensive research showed the problem's severity. Zebra mussels have dramatically changed the Great Lakes by increasing water clarity. In Lake Erie, water clarity has risen from about 15 centimeters to as much as 9 meters in some areas, and in parts of Lake Michigan, water transparency has doubled. This change is due to the mussels’ ability to filter up to a liter of water each day, removing nearly all microscopic plankton. As a result, phytoplankton levels have dropped by about 90%, disrupting the food chain. Native species that rely on plankton, such as fish larvae and planktivorous animals, have been affected, and this has also impacted commercial fisheries that depend on these species. The increased water clarity has also led to more sunlight reaching the lakebed, promoting the growth of filamentous algae like Cladophora. This type of algae consumes oxygen and can harbor bacteria that cause botulism in birds that eat fish. Additionally, zebra mussels have clogged intake pipes at water treatment plants, power plants, fire hydrants, and even nuclear reactors, leading to expensive repairs. The economic impact is significant, with estimated annual costs in the U.S. reaching about one billion dollars. Some experts predict that costs could rise to between two and five billion dollars over ten years. In Canada, an Ontario power company spent up to ten million dollars on chlorine to prevent mussels from accumulating near intake pipes. While chemical treatments like chlorine are still used, they are becoming more restricted due to environmental concerns. Other methods, such as infrastructure changes inspired by European practices, filtration systems, ultraviolet light, anti-adhesive coatings, and mechanical cleaning, are also being employed. Despite these efforts, zebra mussels have not been eradicated and remain a permanent part of the Great Lakes ecosystem. Their spread has reached 32 U.S. states, and a closely related species called the quagga mussel has been found in 19 more states. A cousin from Asia, the golden mussel, was recently spotted in California at the end of 2024. In response, the U.S. federal agency responsible for major dams has launched an innovation contest with a prize of $200,000 to develop new ways to combat these invasive species.