First added to lakes and rivers hoping to improve habitats for fish, the water hyacinth (Eichhornia crassipes) proliferated in mild-winter climate regions to become a nuisance weed. With attractive lavender-blue flowers, the plant has fibrous roots and air-filled buoyant stems and glossy rounded leaves---lovely in an ornamental garden pond but troublesome in natural waterways. Water hyacinth potentially survives year round in USDA hardiness zones 8 and warmer, and its seeds remain viable for up to 20 years.
Water hyacinth grows rapidly to potentially create expansive colonies of interwoven floating plant mats. Large quantities of plants impede natural drainage regimes, causing flooding or delaying the drop in passing floodwater levels. The floating vegetation matrix prevents easy navigation by boats across the lake or canal, and even birds may be prevented from swimming atop the water or wading into areas where the water hyacinth blocks access to water and underwater food sources.
Dense mats of water hyacinth block sunlight to submerged plants resulting in lower levels of oxygen in freshwater. Excessive shading of the water surface leads to lower water temperatures. The plants also slow water flow, potentially causing more settling of water silt and vegetative debris than usual on the lake or river bottom. This results in shallower depths. These plants relish nutrient-rich water and remove phosphates and nitrates, effectively cleaning the water.
Reduction of oxygen levels in freshwater from infestations of water hyacinth affect the base of the food chain. Low oxygen levels reduce the number of phytoplankton present, the food for many freshwater invertebrate animal species. Fish, in turn, eat small invertebrates. Birds, reptiles and humans feed on fish. Moreover, the drifting mats destroy native plant and animal habitats by physically pushing or choking out competitors. Any wildlife dependant upon the native flora and fauna for food must search elsewhere for sustenance or habitat.