Over the years, other species of fish, like koi and goldfish, have become a popular choice to introduce to ponds because of their attractive appearance. Although they may look nice, the damage that these species can cause to a pond ecosystem can be detrimental and costly over a long period of time. Both are considered invasive and can be a nuisance to all other aspects of a pond. Goldfish can grow surprisingly large and have habits like digging up the bottom of ponds and uprooting plants, which can destroy pond liners and affect water quality. Their populations can quickly multiply, making their effects on a body of water exponential if they aren’t dealt with quickly. Koi have large appetites, which can cause them to eat an excessive amount of aquatic plants. Over time they can demolish a food source that other animals rely on. They also have habits of disturbing sediment and plant roots at the bottom of ponds, which makes the water murky and of poorer quality. There are also a few forms of harmful bacteria that tend to thrive in Koi environments. One of these is Aeromonas hydrophilia, which can cause gastrointestinal and urinary tract infections if exposed to the bacteria for long enough. Later down the line, the bacteria that thrive in and around Koi can cause long-term health complications to anyone exposed to it for long enough.