Zebra Mussel
Since about 1769, Zebra Mussels have been considered an invasive species. They are considered an invasive species for many reasons. They consume food, deposit feces on the lake floors, attach themselves to rocks and sometimes even on clams, which leads to their death. Zebra Mussels have even lead to the near extinction of native American Clam colonies in Lake Erie by attaching themselves to them and slowing them down by reducing their ability to feed, thereby killing them. As they are killing other species, they are also reproducing at a rate of almost 1 million eggs a year (although not all hatch). They disrupt the ecosystems by monotypic colonization, and damage harbors and waterways, ships and boats, and water treatment and power plants.The zebra mussels also cling on to pipes under the water and clog them.
Gar
Gars tend to be slow-moving fish except when striking at their prey. They prefer the shallow and weedy areas of rivers, lakes, and bayous, often congregating in small groups.They are voracious predators, catching their prey with their needle-like teeth, obtained with a sideways strike of the head. They feed extensively on smaller fish and invertebrates such as crabs. Gars are found across all of North America (for example Lepisosteus osseus). Although gars are primarily found in freshwater habitats, several species enter brackish waters and a few, most notably Atractosteus tristoechus, are sometimes found in the sea. Some gars travel from lakes and rivers through sewers to get to ponds.