larval drift in river systems or fishing and boating activities that allow for overland transport or movement between water basins. The success of overland transport of Dreissena species depends on their ability to tolerate periods of desiccation, and results suggest that given temperate summer conditions, adult Dreissena mussels may survive 3-5 days of aerial exposure. Quaggas are prodigious water filterers, removing substantial amounts of phytoplankton and suspended particulates from the water. By removing the phytoplankton, quaggas, in turn, decrease the food source for zooplankton, therefore altering the food web. Impacts associated with the filtration of water include increases in water transparency, decreases in mean chlorophyll concentrations, and accumulation of pseudofeces. Water clarity increases light penetration, causing a proliferation of aquatic plants that can change species dominance and alter the entire ecosystems. The pseudofeces that are produced from filtering the water accumulate and impact the environment. As the waste particles decompose, oxygen is used up, water acidity increases (decreased pH), and toxic byproducts are produced. In addition, quagga mussels accumulate organic pollutants within their tissues to levels more than 300,000 times greater than concentrations in the environment, and these pollutants are found in their pseudofeces, which can be passed up the food chain, therefore increasing wildlife exposure to organic pollutants. Another major threat involves the fouling of native freshwater mussels. Since quaggas were discovered in Lake Michigan in 1998, plankton rings formed by the passage of storms have been eaten away by the quagga mussels, threatening the local ecosystem. Each coin-sized quagga can filter up to a liter of water per day, stripping away the plankton that for thousands of years directly and indirectly sustained the native fish. Much of that food supply has now been sucked to the lake bottom; for every pound of prey fish swimming in the lake today, an estimated three to four pounds of quaggas are clustering on the lake bed. Dreissena'''s ability to rapidly colonize hard surfaces causes serious economic problems. These major biofouling organisms can clog water-intake structures, such as pipes and screens, therefore reducing pumping capabilities for power and water-treatment plants, costing industries, companies, and communities. Recreation-based industries and activities have also been impacted; docks, breakwalls, buoys, boats, and beaches have all been heavily colonized. Many of the potential impacts of Dreissena are unclear due to the limited time scale of North American colonization. Nonetheless, the genus Dreissena clearly is highly polymorphic and