Reduce natural biodiversity
Biodiversity" refers to the biological diversity of all forms of life. Essentially, invasive species reduce biodiversity by competing with native species for resources and thereby eliminating them from the genetic pool, which reduces the larger diversity of species.
Degrade ecosystem functions
"Ecosystem functions" refers to the activities of organisms in an ecosystem that are necessary to sustain life, e.g. feeding, growing, moving, excreting waste, and the effects these functions have on the corresponding conditions of their environment. In our natural world, everything is connected to everything else.
When one aspect of an ecosystem is affected, it creates a domino effect resulting in many unforeseen changes. For example, nuisance plant invasions can degrade water quality by blocking photosynthesis, which greatly reduces oxygen levels in the water. This creates a cascading effect by reducing other underwater life such as fish and other plants.
Make lakes and rivers unusable for recreational and commercial activities
Some harmful, non-native plant species are so detrimental that they completely cover the waters they invade. Waters become so choked that it is practically impossible to get water craft through and there is no open water left for swimmers to enjoy.
Increase operating costs of drinking water plants, power plants, dam maintenance and industrial processes
With the spread of harmful, non-native plants and animals in areas such as the Great Lakes, many industries have had to develop costly control methods to maintain their water intake systems.
Certain species can easily colonize on structures like those used for power and municipal water treatment plants, thus reducing pumping capabilities and in some cases resulting in occasional shutdowns.