Written by: Reid Van Kuren, Andrew Base & Arden Ehrenberg

Historical Profile of Water Hyacinth, (Eichhornia crassipes) :

The origins and expansion of Water Hyacinth, (Eichhornia crassipes) are largely agreed upon by experts as having expanded from tropical South America (Kaufman, 2007). The evidence is not only fossil based or calculated by its preferred habitat, but was clearly recorded through trading documents and expedition journals from the late 1800’s  as natives from the amazon region began to explore and trade with their northern neighbours (Day, 2003). Water Hyacinth plants would be brought along on expeditions to be used for medical purposes. As settlers, explorers, and traders utilized and discarded these plants, the theory is that the plant waste would have been introduced to many aquatic and semi aquatic ecosystems across North America. (Castello, 2010). Some of these areas include the southern states of Texas, Louisiana, and Florida. Since Water Hyacinth’s ideal temperature range is 25-30 °C, these perfect climate conditions, combined with vast water bodies, likely allowed it to spread to water basins not directly visited by travellers. Water Hyacinth is considered extremely aesthetic and was often traded to settlements or offered as prizes (Day, 2003). These are the same criteria which allowed Water Hyacinth to expand to Africa, South Asia, and Australia in the 1880’s, and the Congo and river Nile in the 1950’s. Not only would these areas meet the Water Hyacinth species preferred growing conditions, but would have likely been used for the same purposes since it would have been impossible for Water Hyacinth to naturally disperse that far. (Castello, 2010).

Currently, Water Hyacinth is found around the entire world in both freshwater and salt water locations, often in slow or stagnant water basins. Since it can survive or thrive in the min/max range of 12-35°C, the only places Water Hyacinth is not found are polar and sub-polar regions. For example, Russia, Norway, and most of Canada are too cold for its growth and therefore do not need to worry about its invasive nature. Water Hyacinth has been found in Southern Ontario however, as it shares the same climates as Michigan or Maine.


Ecological Connections

Water Hyacinth has earned the title as a nuisance species for the same reason as all other pest species – it’s negative and destructive effect on human inhabited areas. While the ideal temperature for Water Hyacinth is 25-30 °C, it can grow rapidly and withstand temperatures as low as 12°C and high as 35°C, meaning it has a broad temperature tolerance.  Water Hyacinth is known as an r-strategist species; it grows rapidly, and as a species it is tough to kill. While not all invasive species are considered nuisance species, Water Hyacinth shares many human-favoured habitats, such as saltwater shorelines, or freshwater rivers, streams, and lakes. The plant has caused problems for boaters, fishermen, and hydro generation as it outcompetes local organisms, gets caught in nets, lines, engines, and water passages (Oyani, 2011).

Water Hyacinth will grow in warm and stagnate or slow moving water, but it can also survive colder and faster moving waters. It may not grow in this situation, but it will survive and it will travel until more favourable conditions are found. Water Hyacinth reproduces using two methods. The first, is its typical r-strategy of reproduction, meaning each plant will send out hundreds of seeds to cultivate in the surrounding ecosystem. Many will die or fail to take root, but some will survive and cultivate, forming new plants along the shore, or in rich soils (Oyani, 2011). The other is its ability to reproduce vegetatively. Rather than rely on seeds, Water Hyacinth will sprout lateral shoots, which form stems, and fan out into new plants creating a mat (Castello, 2010). This process is repeated until all the surface water is covered, or the plant is damaged/destroyed enough to prevent it. If Water Hyacinth is not managed, or there is not a natural hindrance to its growth, the surface mat will eventually block out the sun, preventing underwater species from receiving energy. Once this occurs, photosynthesis decreases, oxygen levels decrease, and underwater organisms will die. Water Hyacinth is also known to choke out shoreline plants.

Assessment of Management Options

There are typically four primary management strategies used to combat Water Hyacinth around the world: Herbicides, machinery, manual removal, and competing species introduction. It is important to note that in nearly all situations and countries around the world, management strategies have failed. Despite research, monetary investment, and various tactics used by multiple governments and industry experts; existing methods have often been insufficient to contain the aggressive propagation of the weed and viability of its seeds.(Gichuki, 2010).

Even though Water Hyacinth can find preferred growth conditions across the equatorial zones, not all cultures have the same opinions or issues with Water Hyacinth. In Brazil for example, there is a local beetle called the N. buchi, which feeds on Water Hyacinth and is able to curtail the spread and reduce its abundance to less destructive levels (Richardson, 2003). By keeping shorelines clear, and allowing patches to form in the mats, aquatic ecosystems can still perform their functions unimpeded. In New Zealand and controlled parts of the U.S., Water Hyacinth is cultivated for medicinal purposes, similar to the pioneers of the late 1800’s, but on a much grander scale (Richardson, 2003).

For areas without a natural management option, the effects of Water Hyacinth can be much more severe. In Kenya, local fisherman and boaters require passage and the ability to fish for their livelihoods and survival. The government there has spent millions building and using machines to “chew up” the mats of Water Hyacinth, but these efforts have failed as the plants regrow and expand too quickly, and the costs of the operations become too much to be worthwhile (Oyani, 2011). There has not been a proven management strategy yet in Kenya.

Regarding herbicide, pesticide, and other chemical use; this method is considered cheaper, but also risks degrading soil and water quality through contamination, and risks bioaccumulation. Different chemicals such as Glyphosate and 4-D acid have been used in Ontario, but due to the volume and resilience of Water Hyacinth, the use of chemicals cannot keep up with the spread of this water weed (Gichuki, 2010). While the results are effective and immediate, the adverse effects on other organisms is often too great a risk.

Perhaps one of the biggest failures in management practices is the lack of cooperation and unification among communities. Despite being a banned aquatic species across the United States, Africa, and other countries – Water Hyacinth is still grown recreationally in private ponds, or sold in nurseries (CLOC, 2015). The combination of the above failures, mixed with the unwillingness from the community suggests another management option: do nothing. For the time being, Water Hyacinth may be a species that is best dealt with by accepting its resilience, and only taking action in the most required or extreme cases where the most harm is occurring.

Table 2. Management methods and evaluations for  Water Hyacinth

Management Method Direct Costs Benefits Drawbacks Efficacy
No Action N/A N/A Continued spread and nuisance.
Herbicides & Chemicals $ Targeted eradication. Contamination, and reduced water and soil quality. +
Manual Removal $ Safest route. Confirmed removal of species. Not effective. Species will regrow too quickly, or return. +
Machine Removal $$$ Quick and efficient. Environmental damage, costly, ineffective. +/-
Alternative Species $$ Natural and effective control of species. Unintended consequences, i.e. damage to other species or ecosystems. ++/–

Historical Profile of Water Lettuce, (Pistia stratiotes)

Historically, water lettuce has become widely distributed throughout the world due to its wide range of use as an ancient medicine, and as such, it is believed that it had been brought along with migrating human populations as they moved from one region of the world to another (Sculthorpe, 1971). Being a plant that reproduces vigorously in tropical and sub-tropical climates, it quickly spread and established large colonies once introduced to areas where it could easily sustain itself. Likely originating from Africa and South America, the water lettuce soon began to establish itself in Central Asia, South East Asia, most Oceanian Countries, southern Europe and finally in Central America along with parts of North America (Langeland, 1998) (EddMaps, 2017). This is largely due to the increase in commercial shipping, as it is hypothesised that cargo ships had the potential to carry water lettuce seeds in their ballasts (OFAH/OMNR, 2012), resulting in the wide dispersion of this aquatic plant species. Eventually, people began to use this plant decoratively in theirs garden gardens, aquariums and ponds, further exacerbating the spread of this plant beyond the sub-tropical range that it had previously occupied.


Currently, the presence of P. stratoites is recorded in the northeastern region of the United States and in southern Ontario. This eventual migration northward has been recorded in “ponds connected to the Rideau Canal near Ottawa, and in the Welland Canal in the Niagara Region, Lake St. Clair and its tributaries, Bronte Creek in Oakville, and beaches east of Toronto” (OFAH/OMNR, 2012). In addition, its current distribution is also partially due to warming temperatures, and milder winters.

Since the P. stratiotes is not listed on the Invasive Species Act as a regulated or restricted plant, it is common for aquarium and pond stores to sell them. In fact, according to a study conducted near Lake Erie and Lake Ontario, 20% of aquarium and pet stores carried P. stratiotes (Rixon et al, 2005). This contributes greatly to its current spread, as owners of ponds and aquariums may improperly dispose of the plants, which may end up in the Great Lakes or their watersheds. Listed as having an extensive invasion history, according to the Great Lakes Aquatic Nonindigenous Species Information System (GLANIS) water lettuce has a “moderate probability of establishment if introduced to the Great Lakes” (Baker, 2015).

Ecological Connections

As it is known that water lettuce forms dense mats within water ways, it has strong potential to clog them, making recreational activities such as swimming fishing and boating difficult. In areas where water lettuce have formed these large mats, it also blocks out sunlight and in turn, reduces the amount of dissolved oxygen within the water. This makes it very difficult for other aquatic species to survive, especially since this plant is known to consume high quantities of nutrients from the water that it floats on. Not only do these large colonies make habitat less suitable for organisms which occupy the aquatic landscape, but they also block access to water for terrestrial animals (Baker, 2015). To add to this, P. stratiotes colonies can reduce water temperatures, reduce pH, and reduce oxygen mixing with surface wind. As a result, due to these limiting factors, P. stratiotes has the ability to kill native plants, fish and other wildlife in the area that it occupies (Attionu, 1976).

Critical Assessment of Management Options

There are several management strategies already put in place for dealing with non-native water lettuce in ecosystems around the world. Such strategies include the physical removal of the plants from their environment, utilizing other organisms who feed on this plant in order to eradicate it, chemically managing the species population through the use herbicides and cultivating the invasive species for commercial use. The success of these methods are all dependent on the particular location of the habitat, and other limiting factors such as accessibility and sensibility of the ecosystem. Figure 3 demonstrates a condensed version of the benefits and drawback of each strategy. The following is a descriptive list of the possible management strategies:

Chemical Control

The use of herbicide is certainly an effective way to eradicate floating plant matter, although since we are dealing with an aquatic ecosystem, the targeted species may not be the only one affected. Common herbicides such as Glyphosate and Diquat can cause massive weed die-off where the subsequent decomposition may end up removing much of the dissolved oxygen from the water (Baker, 2015).

Biological Control

There has been research conducted to determine if biological controls such as specialist herbivores, meaning organisms who require specific habitat requirement, can be used to eradicate or at least lessen population numbers of P. stratiotes. Species such as the water lettuce moth and the water lettuce weevil feet uniquely on this one plant, and have been used to control this plant in areas where it was not native (Cilliers, 1991). Within 12-18 months the South American water lettuce weevil was able to eradicate at least 40% of the water lettuce in Australia, where it was introduced (Harley et al., 1990). The issue with this approach is that introducing foreign species to a new environment has potentially disastrous consequences. It is very difficult to predict how a non-native species will interact with a new environment. This may not be the best approach for controlling water lettuce in southern Ontario.

Physical Control

To put it simply, this involves the physical removal of the floating plant from the ecosystem. This can be dealt with on a smaller scale by using a small boat, a rake and a bucket to collect the plants, or on a larger scale, through the use of mechanical harvesters. This generally makes for an effective management strategy, as it is a relatively non-invasive procedure concerning the health of the ecosystem. A concern with this method is that since removal boats will be passing through water lettuce patches, there is a risk that these vessels may serve as vector for seeds to “hitchhike” on, thus spreading to other locations.

The following video is a demonstration of how easy it is to conduct physical removals of water lettuce and water hyacinth in London, Ontario, at the Westminster pond. The Upper Thames River Conservation Authority monitors local water bodies for invasive species and

Physical Control with an Economical approach

If these plants can be harvested effectively, its nutritional and medicinal benefits could be put towards good use. Water lettuce contain high concentrations of protein, carbohydrates and fiber and is known to have anti-fungal and anti-microbial properties.  If there is no interest in the food or natural medicine market, they can be used to feed livestock as the plant is known to be fed to pigs. There has also been research into the use of this plant as bio-fuel in areas where water lettuce has overwhelmed certain river systems (Mishima et al. 2008).

Table 3. Management methods and evaluations for  Water Lettuce

Management Method Direct Costs Benefits Drawbacks Efficacy
No Action N/A N/A Continued spread and nuisance.  —
Chemical Control $$ Efficient eradication of species. Contamination, and reduced water and soil quality. May be costly if there is a need for remediation. +/–
Biological Control $ Efficient eradication of species at a low cost Unpredictability of the newly introduced species +/–
Physical Control $$$ Quick, efficient and effective. May spread the species to other locations. Costly. +/-
Physical Control with an Economic Approach $$ Quick, efficient and effective. Economic gain from species removal May spread the species to other locations. ++/-


Management Plan

This management plan provides detailed information regarding the most effective management option that involves the least risk to the environment and the general population. Based on the benefits outweighing the costs, it is determined that the physical removal of the plant is the most effective option for control, as long as a small, but closed, market can be built around the removal of the water lettuce. In this case, a closed market is a market in which profit is solely made for the progress of the management strategy.  This approach is the most viable method, since as much of the removed water lettuce can be sold as feed for livestock like cows and pigs, or even be used as a biofuel (Mishima, 2008) additive. Money generated from the sales of this plant can be used as a way to provide more funding towards management resources such as labour and equipment. This system does not create an increasing demand for the product, and would therefore does not necessarily create another market for the plant. If the plant was sold for potential medicinal properties after it’s harvested from targeted sites, there could possibility be an increase in demand for the product and would therefore contribute to the spread of water lettuce in southern Ontario. Previously, in Ontario (Azan, 2015) and in the southern United States (Langand, 1998), the physical approach has been implemented and seems to be the main tactic used my organization in North America.

In addition o this approach, the issue must also be addressed from a different angle. Not only does water lettuce need to be removed from bodies of water in southern Ontario, but the driving factor for its introduction to water ways must be diminished. Seeing that water lettuce is most commonly introduced to the natural environment via decorative ponds or aquariums, a public education plan must be set in place in order to engage communities in the prevention of its propagation and to encourage pond and aquarium business’ to stop selling water lettuce. Programs such as volunteer based river clean-up or invasive species bio-blitzes could be organized in partnership with organizations such as the OFAH of Ducks Unlimited. To add to these programs, pubic education nights and conferences can be hosted, along with efforts to build public pressure upon local governments to take action against the newly emerging invasive species. Strong social media can also reach many targeted interest groups across a broad platform.

Legal Factors

There are no laws conflicting with the physical removal of the invasive species, as it does not negatively impact the quality of the water that the invasive species resides in. Though in order to put more pressure on local and provincial governments to take action, the Clean Water Act (S.O. 2006, Chapter22) can be used as a stepping-stone towards involving communities in the management project. This act requires communities to monitor existing and possible threats to waterways, and to implement necessary actions to diminish the threat. It allows for public participation on all levels, in order for everyone to get the opportunity to play a role in the planning process of any mitigation or prevention plan against the invasion of water lettuce for example. Finally, and most importantly, the Clean Water Act of Ontario requires that all plans and projects must be “based on sound science” (Clean Water Act, 2006). In turn, the Provincial government of Ontario will have more reason to add water lettuce to the Invasive Species Act’s list of invasive species.

Potential Challenges and Solutions

Even if this management project may seem simple and small in scale compared to other efforts focusing on more prominent invasive species, such as giant hogweed and asian carp, this plan still faces many challenges. Most importantly, the issue of funding poses as the largest hurdle in this project. Without any form of income or outside support, no action can be taken against the spread of water lettuce in the waterways of southern Ontario. Secondly, industry that supplies water lettuce is to root cause of its current spread throughout natural water bodies in our region. Actions must be put in place in order to limit the sale of, or at least discourage these industries from selling water lettuce. Finally, in order to highlight the importance of the current issue facing water lettuce in southern Ontario, public knowledge and education programs must be put in place. This will prove to be one of the most important factors that will allow us to reduce the dispersal of the invasive aquatic plant. The following graph highlights the issues, their challenges and the potential solutions that are suggested in order to effectively coordinate a management strategy against the spread of water lettuce.

Table 3. Funding, public awareness of the issue and the water lettuce industry are the most prominent issues facing the management of water lettuce in Ontario.

Issues Challenges Solutions
Funding The challenge is finding the funding to pay for labour, equipment and other necessary resources required for managing the invasive species. -Selling collected water lettuce as biofuel or even as live stock feed.

-Running volunteer and community based programs in order to deal with the issue in a cost effective manner.

-Gain support from local government, in order to receive funding.

-Apply for grants.

The Water Lettuce Industry The decorative pond and aquarium industry is largely the reason whywater lettuce has spread so much in southern Ontario. The sale of this plant is not under any form of control. -Educate the general public about the issue.

– Social pressure from communities for stores to halt the sale of water lettuce may be effective on the small scale.

-Lobbying to add the plant on the Prohibited List of the Invasive Species Act would have the largest impact.

Lack of Public Knowledge Reaching out to a broad range of individuals may prove difficult. Engaging communities may be even more difficult to accomplish -Hold conferences

-Organize shoreline clean-ups and bioblitzes

-Develop a strong media presence.

-Develop partnerships with organizations such as Ducks unlimited or OFAH.




The physical removal of water lettuce paired with the establishment of a public education program is the ideal method for addressing the spread of water lettuce. This multi-faceted approach tackles the current issues that water ways in Southern Ontario face in regards to water lettuce, and also addresses the main source of the spread of the plant. Since this plan involves sound scientific research, community involvement and sound ecological practices, this management plan will ideally be successful upon its undertaking.



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