The Continual Wrath of Water Hyacinth in Lake Tana

The rapid invasion of Water Hyacinth plant threatens the Ethiopian lake

By Ava Castanha

Water Hyacinth weed is one of the top ten invasive species in the world, given its extremely quick expansion rate of doubling its biomass every five days.
Each water hyacinth plant contains 4,700 seeds, which explains the crazy regeneration of the weed. With a dynamic movement, the weed moves quickly- on a daily basis- by wind and wind-induced wave direction.
Water hyacinth is extremely damaging to the aquatic ecosystem because it forms a “thick floating mat on the water surface that tends to reduce sunlight penetration and the exchange of gases between the water surface and the atmosphere

“It has been a disaster for us,” a local fisherman, Getalew Meteku, said about the invasive weed that has infested Lake Tana. Since 2011, the aquatic plant has haunted the Lake, complicating daily life for the community members.

“We used to have 117 boats for fishing, before the invasion of the lake by the weed. We had work; our situation was better. After enboch invaded the lake, problems started and we had to stop fishing. A lot of us became jobless.”

The community’s livelihoods have been destroyed, and this is only the tip of the iceberg.

Lake Tana is the largest lake in Ethiopia, providing about 50 percent of Ethiopia’s freshwater. It’s also the source of the Blue Nile, which supplies about 60 percent of water to the entire Nile River. The lake supports Tana Beles Integrated Hydropower, the largest energy source for the country. Registered as a World Natural Biosphere Reserve heritage by UNESCO in June 2015, Lake Tana has cultural, historical, and environmental significance.

“A thick floating mat”

Water hyacinth (known as enboch to locals) is a perennial, free-floating aquatic plant, with unique qualities: The weed is one of the top ten invasive species in the world, given its extremely quick expansion rate of doubling its biomass every five days. Each water hyacinth plant contains 4,700 seeds, which explains the crazy regeneration of the weed. With a dynamic movement, the weed moves quickly- on a daily basis- by wind and wind-induced wave direction.

Water hyacinth is extremely damaging to the aquatic ecosystem because it forms a “thick floating mat on the water surface that tends to reduce sunlight penetration and the exchange of gases between the water surface and the atmosphere,” according to a 2020 study by researchers at Bahir Dar University in Ethiopia. This can lead to the concentration of oxygen in the water being dangerously low (called a hypoxic zone), which is deadly for certain aquatic organisms.

Water hyacinth has wide implications: destroying fisheries, maize, and rice crops – as well as negatively impacting tourism, irrigation, transportation, water quality, aquatic biodiversity, and animal grazing in the flood plains.

Impacts on locals

Seye Unetu, an agricultural worker and coordinator in the Ferka Dangwe district,where the invasive species has been particularly damaging, said that the weed has caused several economic and social problems for local residents.

“Because of the weed, we face a lot of economical and social problems. We are not able to use the lake for irrigation and we cannot give enough water for our animals… Without water, we can not work on our farmlands and harvest our crops,” Unetu told Les Voix du Nil (Voices of the Nile), a project spearheaded by two videographers traveling around the Nile Basin.

A 2020 study titled Potential of Water Hyacinth Infestation on Lake Tana, Ethiopia found that the north and northeastern parts of the lake in particular are highly susceptible for invasion. The study revealed that Lake Tana is the perfect storm for the weed, given the lake’s pH, phosphorus, nitrogen, salinity, and water surface temperature conditions, which are all highly suitable for the growth of water hyacinth.

Another 2020 study titled Spatial and Temporal Dynamics of Water Hyacinth and Its Linkage with Lake-Level Fluctuation found that lake-level fluctuations can have an adverse impact on the expansion of the weed. The study provided information on monitoring and evaluating the weed’s growth, which helps stakeholders make decisions about limiting the weed’s expansion.

Due to continual efforts by the local community and the government, the study found that the rate of expansion of water hyacinth was decreasing in 2019 – the expansion rate in 2019 was 23 percent, compared to 120.5 percent in 2016, according to the study led by Minychl G. Dersseh, et al. While this may seem like good news, the maximum lake surface area covered by the weed has remained somewhat constant in the last five years (3,069.3 hectares in 2015 compared to 3,056.3 hectares in 2019).

The study also showed that the post-rainy season is the peak season for water hyacinth expansion, since when the lake level increases, the lake water expands to the floodplain. The Northeast shore of the lake is the most suitable area for the growth and expansion of water hyacinth, because the floodplain is shallow and rich in sediment deposit.

In the most recent documentary produced by Les Voix du Nil, “Nile Story — Episode 4: Saving the Source”, Voices of the Nile remains true to their name and highlights the voices of fishermen, farmers, community members, and a local scientist to convey the threat of water hyacinth and the disruption to daily life that its invasion has caused.

Three years ago, InfoNile published an article highlighting the invasion of the weed on the lake and explaining the impacts of the weed on fishing and agricultural livelihoods, the threat posed to aquatic biodiversity, and urban and agricultural pollution that aided water hyacinth’s unparalleled growth. The status of the weed, however, doesn’t seem to be getting better according to the data on water hyacinth expansion, despite the removal efforts enacted.

Removal, upcycling and restoration

Scores of community members are involved in removing the weed, an industrious, time-consuming labor. They either pull it by hand or operate a machine with a metal board that dives into the water, pulls up the weed and disposes it on the shores.

Dr. Ayalew Wondie is an Associate Professor of Aquatic and Wetland Science at Bahir-Dar University. He emphasizes the importance of empowering the community to become self-sufficient and sustainably maintain the lake for future generations.

He explains that farmers have not been utilizing the dry matter of water hyacinth, which can be made into fertilizer, due to a lack of awareness.

“They have to be aware; their perception should be changed. That’s what we call empowerment,” Wondie said. The weed dry matter is currently being burned after it is pulled up.

The problem isn’t Lake Tana, he said. The source of the problem is in the catchments in the mountains – an area where all the water flows into a single stream, as pollutants get into the watershed via urban pollution or agricultural runoff (pesticides and fertilizers).

Therefore, integrated watershed management serves as a solid solution to maintain a healthy lake. This is a strategy that involves restoring soil health through establishing new forests on previously deforested areas, restoration via planting native plants, and engaging the community to raise awareness about the unique watershed of Lake Tana.

According to the research, the best approach is utilizing a preventative approach on the western and southern shore, and a control strategy on the north and eastern shore. The coverage of the weed is most minimal in the dry season (February through April), thus removing the weed in this time period is advised.

The local fisherman said, “To remove this weed, we have to stop our home activities… If we remove enboch completely, I hope we will fish again and go back to our normal life one way or another.”