The Parrot-Feather plant is native to South America. It takes its name from the feather-like appearance of its leaves.

This invasive aquatic plant was first introduced to the wild near Washington D.C. during the 1890's. The plant was originally sold for decorative purposes in small ponds and aquariums. This was why it was brought from South America, and it was likely released when some aquariums were dumped in the wilderness.

Its takeover of the waters of the Appalachian Trail is hardly surprising. This is because of its easy reproduction: fragments of this plant that break off can go on to grow into new Parrot-Feather plants. Its seeds and fruits can also be carried by animals when they get stuck to the animals' bodies. In addition, the threat it poses to ecosystems is not considered to be common knowledge, so there are likely still people who dump old aquariums that contain Parrot-Feather.

As of 2010, Parrot-Feather has been found in 26 states. It is a pest species for many reasons. Dangerously, it provides a safe refuge for early-stage mosquitoes. This makes it awfully conducive to the Zika virus and other diseases that mosquitoes can carry. In addition, because of its dense growth, it can outcompete native aquatic plants along the Appalachian Trail. It also tangles the propellers on boats and it clogs drain pipes, thus causing property damage along the trail. 

The Water Chestnut is native to Eurasia. This plant is not to be confused with the Water Chestnut that is used in Chinese cuisine: this invasive variety has the scientific name Trapa natans and it is known commonly as the "European Water Chestnut".

Although its exact date of introduction to the United States (and the Appalachian Trail, by extension) is not clear, it is a fact that this harmful aquatic plant was introduced sometime in the 1870's. Like many other invasive aquatic plants, it was used historically in the United States as a decoration for small ponds. In 1877, it was introduced as a specimen at the Cambridge botanical garden at Harvard. Things soon got out of hand however, as the pest plant soon spread to the Hudson River by the early 20th Century. Because of this rapid spread, the plant now grows in the waters of many states that the Appalachian Trail runs through: from New England all the way down to Virginia.

The aquatic plant grows in dense layers on the water's surface and it carries very few nutrients for either animals and plants. Because of its heavy growth, it can absorb much of the sunlight that native aquatic plants need and it can also take up their space without much to give back to the ecosystem. This puts native aquatic plants on the Appalachian Trail in danger of being outcompeted. It also uses up quite a bit of oxygen in the water when it grows prolifically, which endangers the trail's fish population.

One must also be wary of its fruits: these seed pods have sharp spines on them. This means that the plant can severely injure swimmers and waders who wish to use the waters of the trail for relaxation.