In all gardens there are plants that are best avoided due to their invasive nature. Invasive plants in ponds are a larger danger. Invasive plants invade quickly and may take over a whole pond if not properly isolated and destroyed. In certain areas invasive plants are made illegal, to prevent them from destroying the ecosystem. Invasive plants may reduce oxygen in the the pond, killing not only other plant species, but fish and other aquatic animals.
Contact your local university extension office to learn what invasive plants are common for the area and to receive a field guide for easy plant identification.
Locate plants not bought yourself to identify species you are unfamiliar with.
Determine if the plant is a floating plant, or orginates from the bottom of the pond. Look for flowers that will help you identify the plant. Inspect the leaves for size, how many leaves it has and whether they are compounded or loose. Look at the leave blades for any identifying marks, such as serrated edges or round edges.
Find areas in the pond to determine if any of your own plants are displaced, and replaced, by another plant species. Invasive plants take over quickly.