Water hyacinth, or Eichhornia crassipes (Mart.) Solms, from the family Pontederiaceae, is a free-floating aquatic plant that commonly grows in inland freshwater bodies such as lakes, rivers, streams, ponds and wetlands. The plant has broad, wide canopy-like waxy leaves and purple clustered flowers that grow in spikes. The petioles of the plant appear bulbous with air-sacs that help make it buoyant. The plant varies in height from a few centimetres to nearly a metre, while the leaves may be around 15–20 cm in length and width [14]. The plant can sometimes become rooted when it lodges in muddy, shallow waters and the flowers may be blue or white [14]. With the ability to reproduce both sexually through seed propagation and asexually through stolon vegetative reproduction, water hyacinth exhibits the reproductive characteristics suited to invasive success. According to Zhang et al. [26], the invasive spread of water hyacinth is characterised by its genetic uniformity due to its prolific clonal reproduction, dominated through vegetative propagations. In the absence of interspecific competition, water hyacinth outcompetes other aquatic plants, even outside its native range; thus, its growth is rapid and unchecked. Its seeds can remain viable for up to 20 years and may germinate in moist soil or warm, shallow waters [28]. Additionally, the high dispersal of its buoyant propagules and well-developed phenotypic plasticity and its ability to change in response to different stimuli are among the factors that enhance the plant’s adaptive capacity to any local environmental changes in its native range. Meanwhile, these factors facilitate its ability to colonise its introduced ranges [26].

A study by Wu and Ding [5] discussed the abiotic factors in terms of environmental parameters and the biotic, species-specific factors influencing water hyacinth invasion. Interesting highlights from the abiotic study include the influence that the dissolved oxygen level has on reducing the plant growth, while high levels of conductivity, indicating nutrient availability, promotes the plant’s propagation. Water hyacinth has also been proven to reduce the biodiversity of the invaded area, according to four biodiversity indices. Water hyacinth invasion was observed to reduce the overall biodiversity in terms of species richness and evenness. Various other factors may either promote and accelerate or limit and slow a water hyacinth infestation. These include temperature, nutrients, salinity, light, wind, water currents, carbon dioxide levels, waves, turbidity and changes in water levels [27,29]. In general, higher temperatures and greater nitrogen and phosphorus content are important factors promoting water hyacinth growth [27,29]. Higher salinity levels inhibit water hyacinth proliferation by inducing growth reduction and an increase in its mortality rate [30], which hamper invasions in coastal areas. In cases where both salinity and nutrients vary, nutrients will have a greater influence on the leaf count while total biomass remains limited [30]. A higher flow velocity reduces the probability that water hyacinth can become established. Consequently, a higher level of dissolved oxygen derived from the turbulence similarly limits the plant’s growth. Water hyacinth has also been reported to reduce phytoplankton productivities due to the fall in dissolved oxygen and chlorophyll-a levels in water bodies covered by the plant. These have major ecological impacts on the infested water as the aquatic food web becomes disrupted, leading to a drop in aquatic species composition and biodiversity [31].

Despite the extensive knowledge of the inhibiting factors of the plant, the water hyacinth invasion rate can be uncontrollable, especially when aided by continuous inputs of nutrient pollution from agricultural activities. The mechanical harvesting of water hyacinth requires a weed harvester, an excavator and other heavy machinery. Physical harvesting may refer to the same process or involve manual harvesting. Both the mechanical and physical methods lead to an abundance of harvested biomass that must be managed. In contrast, chemical and biological methods aim to eradicate the weed. Chemical cleansing using herbicides kills the plant but may also affect non-target species [2]. Biological control involves the use of biocides or, more commonly, an insect predator of the plant, namely the weevil beetle. Biocides are not commonly used as they are less commercially available compared to their chemical counterparts [32]. Biological control using the weevil relies on its herbivorous nature to shorten the plant petioles and reduce the above- and below-surface biomass [33]. Although successful in reducing the size and increasing the mortality of the plant, weevil biocontrol fails in reducing the plant cover, one of the most important factors in deterring the invasion [33]. With such different approaches and varying levels of success, controlling water hyacinth invasions clearly requires an integrated approach using all available means to ensure long-term success and to avoid the re-establishment of an aquatic weed invasion.

The invasion of water hyacinth has a major impact on the rural people affected, especially those who depend on water bodies for their livelihoods, such as fishing and riparian communities [7,8,9,20,34]. As discussed by Dersseh et al. [1], a water hyacinth invasion has negative impacts on the hydrology and environment, resulting in subsequent socio-economic impacts, as it disrupts human daily activities and health. The increase in evapotranspiration compared to surface evaporation disrupts the hydrological water balance in the infected areas, which could disrupt local rainfall events. Reduced water flows in rivers due to water hyacinth blockages will promote sedimentation, deoxygenation and water quality deterioration. Weed canopies on lakes reduce sunlight penetration. This increases the water turbidity and reduces variability in temperatures, as well as other similar water quality concerns [35]. Consequently, all these events lead to a reduction in fish and other aquatic organism populations as their habitat becomes less habitable. Instead, the proliferation of disease vectors such as mosquitoes and snails will occur, as the plant hosts a variety of these species [9].

Dense weed mats mean limited access to waterways, leading to conflicts among the affected communities to gain access to watercourses. As water hyacinth is buoyant and not anchored, it moves with the wind. This is especially disruptive to fishermen, making boat navigation harder, delaying fishing preparation and resulting in fishing net entanglements and damage to other equipment [20]. In places with hydroelectric dams, the invasion has led to damaged generators and coolers and threats to the electricity supply [28,36]. Hence, locals’ livelihoods are disrupted as many lose their source of income, incur costs due to damage and are further inconvenienced in many ways.

Coping strategies for water hyacinth invasion can be described as reactive- or recovery-based [34]. Reactive behaviour is a short-term coping mechanism for handling an immediate current situation. Affected communities tend to be reactive, for instance, by joining clean-up activities to remove the weed or simply halting their daily routine during the invasion peak. On the other hand, some communities have been reported to adopt alternative sources of income when interrupted by water hyacinth. Such actions are considered recovery-based, as locals recover their livelihoods through other means, such as switching to agriculture.

From the rural perspective, water hyacinth has only negative impacts on communities, according to a survey conducted on communities affected by an invasion of Lake Tana, Ethiopia [7]. Livelihood security concerns may hinder the prospects for water hyacinth to be explored by a rural community, especially without support from relevant authorities, which can provide information and technical and financial aid [37]. Thus, a community tends to adopt alternatives to overcome its hardship. Consequently, the water hyacinth problem remains unresolved.

Therefore, a community must be empowered so that it becomes resilient in coping with a water hyacinth invasion. The problem tends to recur because fully eradicating the plant appears to be impossible as it rapidly expands its territory. The key to successful community involvement is the dissemination of information coupled with empowerment programmes. These approaches would enlighten locals, offering not only the knowledge but also the skills needed to manage water hyacinth for their benefit. One example of a successful empowering project was reported in Indonesia. The Bangkit Bersama Cooperation, a community empowerment institution, developed a water hyacinth waste scavenger programme in the Saguling Reservoir area that created job opportunities through the utilisation of the weed [38,39,40]. The success of such programmes highlights the importance of integrating the concept of the weed into the community and local livelihoods in order to ensure that its management is sustainable [37].