**4. Environmental and socio-economic risks**

Nowadays, WH weed causes major socio-economic and environmental concerns for millions of people in riparian communities and is, therefore, an added constraint on sustainable development [16, 42]. The common risks associated with WH weed are described under the following subsections and summarized in **Table 2**.

## **4.1 Environmental risks**

WH weed distribution affects the ecological balance and changes natural diversity. These changes threaten the survival of many plants and sea-going creatures since weeds compete with the natives for food, sunlight, and space [6, 16]. This causes an imbalance in the aquatic micro-ecosystem and often means that a range of fauna that relies on a diversity of plant life for its existence will become extinct. Besides suppressing the growth of native plants and birds and negatively affecting microbes,


*c*

*Social risks posed by spread of WH.*

#### **Table 2.**

*Summary of social, economical, and environmental risks of WH infestation.*

#### *Invasive Water Hyacinth Challenges, Opportunities, Mitigation, and Policy Implications… DOI: http://dx.doi.org/10.5772/intechopen.106779*

WH prevents the growth and abundance of phytoplankton under large mats, ultimately affecting fisheries [16, 43]. For example, in Madagascar, many parts of the Alaotra Lake, a site of biological importance, have been reported as covered with carpets of WH that are detrimental to a number of animal species, such as the duck, Thalassornis leuconotus. A recent study in Lake Naivasha showed a massive reduction in the fish population due to reduced oxygen levels, which was attributed to the resurgence of WH [44]. The blockage of waterways by WH increases siltation and hinders activities like swimming, fishing, and sand extraction [1].

Large WH mats prevent the transfer of oxygen from the air to the water surface or decrease oxygen production by other plants and algae [16]. The oxygen dissolvability levels can reach harmfully minimum concentration for fish that are touchy to such changes. Besides, low dissolved oxygen situations initiate the release of phosphorus from the silt, which then quickens eutrophication and can prompt a resulting increment in algal or WH blooms [1]. Death and decay of WH vegetation in large masses deteriorate water quality and the quantity of potable water and increase treatment costs for drinking water [45]. People often complain of localized water quality deterioration [43]. This is of considerable concern when people come to collect water, swim, and wash.

In addition, Amare [46] pointed out that the rate of loss of water due to evapotranspiration can be 1.8 times the same rate of respiration from the water surface, but it is plant-free. This already has major impacts on the area where water is scarce. For instance, it is evaluated that the flow of water in the Nile could be decreased by up to one-tenth because of expanded misfortunes in Lake Victoria from the WH invasion [47]. Thick WH tangles also block canals, waterways, and rivers leading to hazardous flooding. This effect is more aggravated on riparian residents with little capacity to protect themselves from the flood as well as flood-associated risks [48].

## **4.2 Economic risks**

WH infestation can exhibit numerous impacts on the fishing activities; access to destinations ends up troublesome when weed invasion is available, loss of fishing equipment frequently results when nets or lines become tangled in the root frameworks of the weed and the consequence of these issues is, as a rule, a decrease in catch and consequent loss of livelihood [44]. WH floating mats may also limit access to the breeding, nursery, and feeding grounds for some economically important fish species [16]. For instance, In lake Tana, Ethiopia, it is reported that fishermen have reduced their income, reduced fish catch, increased unemployment and reduced resource availability, increased poverty, and reduced efficiency of fishing activity [46]. It is additionally detailed, as in Lake Victoria, fish get rates to reach the Kenyan segment diminished by 45% in light of the fact that WH mats blocked access to fishing grounds, deferred access to business sectors, and increased costs of materials and effort [11]. Similarly, in Lake Naivasha, the WH infestation has been observed to have a negative impact on the economic status of the fishery community [44].

Many large hydropower schemes are also suffering the effects of WH weed infestation [49], WH causes high water losses through evapotranspiration and blocking turbines. For instance, it is estimated that the flow of water in the Nile could be reduced by up to one-tenth due to increased losses from evapotranspiration by WH in Lake Victoria [47]. Furthermore, the Tana Beles hydropower scheme on Lake Tana has suffered the impact of the weed, hence plenty of time and money has been invested to clear and prevent the weed from entering the turbines, which may cause

damage and power interruptions [11]. On the Tana Beles hydropower scheme, the WH caused damage to water coolers and generators, prompting the power utility company to switch off generators for maintenance, and about 15 megawatts of electricity were lost causing a power cut in an urban area of Ethiopia [50].

### **4.3 Social risks**

Water issues determine life and social sustainability. Both in Africa and worldwide, WH weed infestation is interfering with agriculture by closing irrigation and drainage systems and increasing water wastage [7, 11]. WH Floating mats have a significant impact on human life by supporting living creatures that are harmful to human health. For example, in Lake Victoria, the WH free-floating roots and semisubmerged leaves and stems reduce water currents and provide more breeding habitat for the malaria-causing Anopheles mosquito [6, 12]. The tangled weed mat is home to snails that serve as vectors for the Bilharzia parasite and Mansonioides mosquitoes, harmful to human health. WH has additionally been implicated in possession of an agent that causes the cholera virus [1, 6, 11]. For instance, from 1994 to 2008, the state of Nyanza in Kenya suffered from cholera on the border with Lake Victoria. The annual coverage of WH on Lake Kenya has also been directly linked to the number of cholera cases reported in the state [51].

At the local level increased incidences of crocodile attacks have been attributed to the heavy infestation of the weed, which provides cover to the reptiles and poisonous snakes [45, 47]. These impacts pose, especially in the least developed countries, an additional burden on the limited health services and facilities available to the rural communities. In Ethiopia, Senayit et al. [52] reported an increase in malaria incidence and lack of drinking water, whereas during peak infestation periods, the floating weed serves as a host for snakes and crocodiles. Moreover, when the water level decreases, the unpleasant smell from decomposed WH residues disturbs the villagers. WH also impedes the recreational use of rivers and lakes. Decreased recreational and esthetic value are also among the major societal problems caused by invasive WH plants [7].
