water-hyacinth, common water-hyacinth, floating water-hyacinth, Eichhornia speciosa Kunth, Piaropus crassipes (Mart.) Raf.

Nonindigenous Occurrences:

Eichhornia crassipes is found on 5 continents (Lowe et al. 2000). This species has been recorded in New South Wales, Australia (NSW DPI 2012), in the Bahamas (GISD 2006), Bangladesh, Benin (de Groot et al. 2003), British Virgin Islands (GISD 2006), Burkina Faso, Cambodia, Camaroon, Cayman Islands, Chile, southwestern China (Jianqing et al. 2001), Colombia (GISD 2006), the Republic of Congo, the Cook Islands, Costa Rica, Cuba, Dominican Republic, Egypt (Fayad et al. 2001), Equatorial Guinea (GISD 2006), Ethiopia, Fiji, French Polynesia, Gabon, Ghana, Guadeloupe, Guam, Guatemala, Guinea, Honduras, Hong Kong, India, Indonesia, Israel, Jamaica, Japan, Jordan, Kenya (Moorhouse et al. 2001), Lao People’s Democratic Republic (GISD 2006), Lebanon, Liberia, Madagascar, in the Shire River in Malawi (Phiri et al. 2001), Malaysia, Maldives, Marshall Islands, Martinique, Mauritius, Mexico, Federal States of Micronesia, Mozambique, Myanmar (Burma), Nauru, New Caledonia, New Zealand, Nicaragua, Norfolk Island, Northern Mariana Islands, Palau, Panama, Papua New Guinea, Peru, Philippines, Portugal, Puerto Rico, Republic of Haiti, La Reunion, Russia, in Kagera River of Rwanda (Moorehouse et al. 2001), Saint Lucia (GISD 2006), Samoa, Senegal, Sierra Leone, Singapore, Solomon Islands, South Africa (Oberholzer and Hill 2001), in the Guadina River basin, Spain (Téllez et al. 2008), Sri Lanka (GISD 2006), Sudan, Swaziland, Syria, Taiwan, Tanzania, Thailand, Togo, Uganda, United States, United States Minor Outlying Islands, Vanuatu, Venezuela, Vietnam, Zambia, and Zimbabwe.

The first U.S. occurrence was documented from the Southern States Cotton Expo in New Orleans, Louisiana in 1884 (Klorer 1909; Penfound and Earle 1948). Water hyacinth has since spread throughout the southeastern U.S., much of California, the northeastern coastal region, and up the Mississippi River into the Great Lakes region. It further spread to the islands of Puerto Rico, Hawaii, and Guam.

Eichhornia crassipes is a fast-growing, troublesome aquatic plant with global distributions in tropical and subtropical areas of the world (Center and Spencer 1981; Penfound and Earle 1948). Its showy, attractive lavender flowers precipitated this worldwide distribution. Once introduced to a new region, the plant quickly establishes and spreads.  In the absence of a sustained freeze, the plant grows as a perennial.  In its northern range, the plant grows as an annual, where it is either re-introduced or germinates from seed.  Long-term (2-4 week) exposures to temperatures at or near freezing are required to significantly reduce E. crassipes populations (Owens and Madsen 1995; Russell 1942). The plant has a low tolerance for saline waters.  Plants grown in water containing 3% seawater exhibited significant leaf necrosis after 28 days (Penfound and Earle 1948).

Dense, floating mats of E. crassipes and the subsequent build-up of organic detritus in the mat create an environment that supports the growth of emergent aquatic and terrestrial species, including woody species such as Salix spp. and Cephalanthus occidentalis.  These floating islands (also referred to as tussocks, sudds, and flotants), accelerate succession and create concern for navigation and infrastructure (Penfound and Earle 1948; Russell 1942).
Eichhornia crassipes reproduces vegetatively through the production of ramets and an abundance of seeds. Eichhornia crassipes exhibits alternative physiological responses in response to varying nutrient concentrations. Under high nutrient concentrations E. crassipes allocated more energy to asexual reproduction, thus accumulating more biomass. When exposed to low nutrient concentrations, E. crassipes allocated more energy to sexual reproduction and root growth (Soti and Volin 2010). Flowers are known to be pollinated by a number of insects, most notably the introduced honey bee (Aphis mellifera L.) (Penfound and Earle 1948; S.C.H. Barrett).   Seeds remain dormant in the hydrosoil until exposed to a drying event (Penfound and Earle 1948; Gettys 2014). Eichhornia crassipes can double its population in as little as two weeks, creating an enormous amount of floating biomass (Penfound and Earle 1948).  One hectare of healthy E. crassipes can weigh as much as 415 metric tons (Schardt 1997).

Potential pathway(s) of introduction: Dispersal, hitchhiking/fouling, unintentional release, stocking/planting, and escape from commercial culture.

Eichhornia crassipes occurs near waters connected to the Great Lakes basin. This species has been reported to occur in Lake St. Clair and the Detroit River in 2010 (Adebayo et al. 2011). In Michigan, it has been found in Oakland, Livingston, Wayne, and St. Clair counties (Ankney 2012). Clonal individuals of Eichhornia crassipes can disperse to new areas when fragments are transported by water (Masterson 2007). Eichhornia crassipes forms thick mats that can become entangled on to boat propellers and trailers to be spread to other water bodies. For instance, boats coming from water bodies such as Lake St. Clair or the Detroit River may unintentionally transport E. crassipes to Lake Erie.

Eichhornia crassipes is sold at aquarium stores and is sold in the Great Lakes. This species is a popular aquarium plant and is available for purchase in the Great Lakes region. Eichhornia crassipes may be frequently introduced into waterways after disposal of the plant from water gardens (Adebayo et al. 2011). In a survey of aquarium stores near Lakes Erie and Ontario, E. crassipes was available for purchase in 30% of the stores (Rixon et al. 2005). Title 18 U.S. Code 46 states that it is a violation of the law to knowingly transport E. crassipes in interstate commerce, and to sell or purchase the plant (18 U.S.C. § 46). The sale of this species is prohibited in Chicago and Illinois State, but not in Indiana, Michigan, Minnesota, New York, Ohio, Ontario, Pennsylvania, Quebec, or Wisconsin (Great Lakes Panel on Aquatic Nuisance Species 2012).

Greenhouses within the Great Lakes basin commercially culture and sell E. crassipes for use in water gardens, thus, it may escape and spread into larger water bodies. Retailers advertise the E. crassipes as a good oxygenator plant for ponds.

Eichhornia crassipes has a moderate probability of establishment if introduced to the Great Lakes (Confidence level: High).

Eichhornia crassipes has been reported to tolerate salinities of 0-8.8 ppt, with growth rate decreasing with increasing salinity (Rotella and Luken 2012). This species tolerates water temperatures of 5°C for short periods of time (Owens and Madsen 1995) and survives in water temperatures up to 30°C (NSW DPI 2012). Eichhornia crassipes requires abundant nitrogen, phosphorus, and potassium for growth. The abiotic and climatic conditions of the introduced ranges of E. crassipes (e.g. Lake St. Clair, Detroit River, New York) are similar to the Great Lakes. Nutrient inputs to the Great Lakes from runoff may provide the necessary nitrogen and phosphorus levels for E. crassipes growth. Slow flowing fresh water bodies located in the Great Lakes basin may provide suitable habitats for this species.

Eichhornia crassipes is somewhat likely to be able to overwinter in the Great Lakes basin as rooted plants, which are more resistant to freezing temperatures than free floating mats (Owens and Madsen 1995). There is anecdotal evidence that E. crassipes has overwintered in private ponds in Michigan (Ankney 2012). Eichhornia crassipes may experience increased mortality and reduced regrowth after long periods of near-freezing temperatures (Adebayo et al. 2011, Owens and Madsen 1995, Rixon et al. 2005). Climate change may make the Great Lakes more suitable for this species’ establishment. Shorter ice duration and warmer temperatures may improve this species’ ability to survive the winter in the Great Lakes (Adebayo et al. 2011).

It produces seeds that can remain viable for 5-20 years (FAO 2013). Although it is capable of producing dormant seeds, evidence suggests that E. crassipes will not establish a population in the Great Lakes region via sexual reproduction due to the lack of genetic diversity of the introduced populations and the lack of seeds found in the sediment where it has been introduced (Adebayo et al. 2011). Its primary method of spread is through vegetative fragmentation (NSW DPI 2012). This species rapidly grows and can double its biomass every 2 to 34 days (Gutiérrez et al. 2001).

Eichhornia crassipes forms dense stands, which may impact species in the Great Lakes. In San Joaquin Delta, California, insect densities where lower in patches of E. crassipes and there was a difference in insect composition between E. crassipes and the native pennywort (Hydrocotyle umbellata) (Toft 2000). Non-native introduced amphipods such as Crangonyx floridanus were more abundant in E. crassipes stands than in the native pennywort stands, and are not frequently consumed by fish. Fish preyed heavily on native amphipod Hyalella azteca that was more abundant in the native pennywort. It is suggested that the presence of E. crassipes may influence native invertebrate community assemblages. In Lake Okeechobee, E. crassipes displaced native bulrush and shaded out native submerged plants that provide important habitats for fish, waterfowl, and other animals (University of Florida 2013). In Caohai and Dianchi lakes in Yunnan province, southwestern China, E. crassipes had competed with native plants for water, nutrients, and space, and contributed to the reduction in native plant diversity (Jianqing et al. 2001).

Control methods include mechanical pulling, biological control, and herbicide. The most effective control method is 2,4-D herbicide, which kills E. crassipes and reduces the populations of native species to some extent (Ivanov et al. 2007). Surveillance and management efforts are currently underway to detect, control, and/or eradicate this plant in Michigan (Michigan DEQ 2013) and Wisconsin (Falck et al. 2010). However, a basin-wide monitoring program is lacking (Dupre 2011). Michigan has a state management plan to prevent aquatic invasive species introductions, limit their dispersal, and control their populations (Michigan DEQ 2013). The Michigan Department of Natural Resources and the U.S. EPA have an early detection and rapid response plant regarding the establishment of E. crassipes (Ankney 2012).

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Socioeconomic	Beneficial

Eichhornia crassipes grows in thick mats that reduce the light and oxygen availability in the water (Ivanov 2006). After removing E. crassipes from Lake Victoria by cutting, there was a significant increase in dissolved oxygen (Osumo 2001). In Africa, Eichhornia crassipes can be detrimental to water availability due to its high rate of evapotranspiration and its ability to take advantage of scarce water reserves, resulting in an annual loss of 7 billion m3 of water from the Nile River (De Groot 1993, Padilla and Williams 2004). In China, E. crassipes has exacerbated water pollution by absorbing heavy metals and releasing them at death (Jianqing et al. 2001).

In Lake Okeechobee, E. crassipes displaced native bulrush and shaded out native submerged plants that provide important habitats for fish, waterfowl, and other animals (University of Florida 2013). In Caohai and Dianchi lakes in Yunnan province, southwestern China, E. crassipes competed with native plants for water, nutrients, and space, and contributed to the reduction in native plant diversity (Jianqing et al. 2001).

Eichhornia crassipes can potentially alter predator-prey relationships. In San Joaquin Delta, California, insect densities where lower in patches of E. crassipes and there was a difference in insect composition between E. crassipes and the native pennywort (Hydrocotyle umbellata)(Toft 2000). Non-native introduced amphipods such as Crangonyx floridanus were more abundant in E. crassipes than in the native pennywort, and are not frequently consumed by fish. Fish preyed heavily on native amphipod Hyalella azteca that was more abundant in the native pennywort. It is suggested that the presence of E. crassipes may influence native invertebrate community assemblages.

Eichhornia crassipes has the potential for high socio-economic impact if introduced to the Great Lakes.

Eichhornia crassipes can pose a risk to human health by providing a habitat for mosquitos, and may increase the risk of mosquito-borne diseases (Jianqing et al. 2001, Mailu 2001). This species has reduced water availability in Lake Victoria Basin, which led to social conflicts over the lack of clean water (Mailu 2001). In addition, the infestation of E. crassipes resulted in increased transportation costs, blockage of irrigation canals, and difficulties in electricity and water extraction. Due to E. crassipes infestation, the Kenyan port of Kisumu reported a 70% decline in economic activities. This species can impact recreational fishing by making it difficult to access fishing grounds and preventing boating (Mailu 2001, Richardson and Wilgen 2004). 

In Benin, the infestation of E. crassipes was estimated to significantly reduce the annual income of the villagers, who relied on fishing and trade for an income (De Groote et al. 2003). Biological control of the infested waters in Benin was estimated to be US $2.09 million.

Eichhornia crassipes has the potential for moderate beneficial impact if introduced to the Great Lakes.

Eichhornia crassipes is an ornamental plant used in water gardens. Eichhornia crassipes has the potential to be used for bioethanol and biogas production, electricity generation, industrial uses, animal feed, or agriculture (Jafari 2010, Malik 2007). It may be utilized for wastewater treatment or heavy metal remediation (Pinto et al. 1987).

Title 18 U.S. Code 46 states that it is a violation of the law to knowingly transport E. crassipes in interstate commerce or selling or purchasing the plant (18 U.S.C. § 46). The sale of this species is prohibited in Chicago and Illinois State, but not in Indiana, Michigan, Minnesota, New York, Ohio, Ontario, Pennsylvania, Quebec, or Wisconsin (Great Lakes Panel on Aquatic Nuisance Species 2012).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control

Biological
Bioherbicides were developed for use in Florida’s E. crassipes infestation, including the pathogen Cercospora piaropi, the fungus Myrothecium roridum, and the water hyacinth-specific pathogen Alternaria eichhornia (Charudattan 2001). Field studies suggest applications of C. piaropiare with the surfactant Silwet L-77 are effective in reducing the biomass of E. crassipes.

There are currently seven natural enemy insect species of E. crassipes that have been studied as potential biocontrol agents, including two weevils (Neochetina bruchi and N. eichhorniae), two moths (Niphograpta albiguttalis and Xubia infusellus), a mite (Orthogalumna terebrantis), a sap-sucking mirid (Eccritotarsus catarinensis), and a grasshopper (Cornops aquaticum) (Bownes et al. 2013; Marlin et al. 2013; Soti & Volin 2010). The primary biocontrol agents used to control E. crassipes are the Neochetina weevils, but these have been largely ineffective in controlling the spread of E. crassipes in Florida (Center et al. 1999). Weevil herbivory effectively reduces overall biomass, plant size, and vigor, but does not appear to affect plant cover or reduce mat size (Jones et al. 2018).

Evaluations of the efficacy of control methods suggests that utilizing different herbivorous insect species together can be effective in controlling water hyacinth infestations (Bownes et al. 2013; Marlin et al. 2013; Soti and Volin 2010). Weevils alone or weevils and mirids in combination were shown to be the most effective at reducing biomass growth. However, there are multiple parameters that can be used as metrics for evaluating the effectiveness of a biocontrol agent. Each agent or combination of agents do not equally affect each parameter, and the efficacy of certain agents may vary in different environments (Marlin et al. 2013; Ajuono et al. 2009). Ajuono et al. (2009) noted that N. eichhorniae was more effective at reducing E. crassipes growth than the mirid, which is in part due to the different feeding behaviors and life cycles of the two insects (N. eichhorniae is a stem-borer and has a 120-day life cycle, E. catarinensis feeds only on the leaves and has a 3-week life cycle). However, N. eichhorniae are not effective in environments where E. crassipes are seasonally rooted in mud, therefore making the mirid the more effective agent in these environments (Ajuono et al. 2009). Management and control strategies ought to consider the mechanism an agent uses to control E. crassipes, whether the agent or combination of agents are appropriate for a given environment with an infestation of E.crassipes, and what growth parameters would be most appropriate for evaluating the efficacy of the agent.

In South Africa, water nutrient status was found to be more important to water hyacinth growth than was herbivory (Coetzee et al. 2011). Therefore, efforts to control E. crassipes should focus on reducing water nutrient concentration. However, nutrient limitation as the sole control method has proven to be ineffective, but it can significantly reduce growth when utilized in conjunction with intensive herbivory (Bownes et al. 2013; Soti & Volin 2010). Soti and Volin (2010) observed that Eichhornia crassipes exhibited a significant reduction in relative growth rate when exposed to high levels (80% defoliation) of biomass removal in both high and low nutrient treatments. However, they observed no significant reduction in relative growth rate when E. crassipes was exposed to continuous low levels (10% defoliation) of biomass removal in high or low nutrient scenarios suggesting that chronic exposure to low levels of herbivory are not effective at controlling E. crassipes, regardless of nutrient concentration.

Under varying nutrient conditions, the grasshopper Cornops aquaticum, has also proven to be effective at reducing E. crassipes growth. In high (7.6 mg N/L, 1.37 mg P/L), medium (2.5 mg N/L, 0.316 mg P/L), and low (.034 mg N/L, .024 mg P/L) nutrient treatments Cornops aquaticum (applied at a density of 1 insect per plant) reduced plant growth by 67%, 100%, and 400%, respectively (Bownes et al. 2013).

Herbivory is typically more effective in controlling high-density infestations of E. crassipes where the effects of herbivory interact with effects of interspecific and intraspecific competition (Ajuono et al. 2009).

Physical
After removing E. crassipes from Lake Victoria by cutting, there was a significant increase in dissolved oxygen (Osumo 2001).

The efficacy of water level treatments (i.e. drawdowns or shallow submergence) on E. crassipes have been investigated as potential control mechanisms. In subtropical climates, water drawdowns significantly decreases the survival rate of E. crassipes during the winter (mean temperature = 5.5 C). However, in warm winter scenarios (12.4 C) drawdowns were effective in initially reducing overwinter survival but biomass increased overall during the latter growth phase in the spring.  Submergence of E. crassipes also has been shown to lead to higher rates of regrowth in spring. Therefore, drawdowns and submergence are not effective in long-term control of E. crassipes in subtropical climates (Liu et al. 2015). Additionally, water level treatments may not be effective in temperate regions like the Great Lakes where the harsh winters likely would cause annual die-offs of E. crassipes followed by the potential germination of a seed bank in spring (MacIsaac et al 2016; Owens and Madsen 1995).

Chemical
The herbicide 2,4-D kills E. crassipes and reduces the populations of native species to some extent (Ivanov et al. 2007). Note: Herbicides may limit the effectiveness of herbivorous insects in controlling and limiting E. crassipes growth and spread. Center et al. (1999) suggested that the ubiquitous application of herbicides may lead to a continuous lag phase for population growth of biocontrol agents, but the water hyacinth has been hypothesized to readily re-establish from abundant seed sources after herbicide treatment.

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.