The outlet of the Blue Nile River. Photo by Richard Mortel via Flickr. CC BY 2.0

Since 2012, an invasive weed known as the water hyacinth has been subsuming tens of thousands of acreage of the surface of Lake Tana, as well as adjacent wetlands and ranches surrounding the lake.

About two million Ethiopians directly depend on the lake as well as adjacent wetlands and ranches for their livelihood, according to Nature And Biodiversity Conservation Union (NABU), a German non-governmental organization focused on sustainability and conservation in the region. The steady growth of the water hyacinth has taken a toll, particularly on the western side of the lake, an area populated by fishermen, farmers, and ranchers whose work depends on it.

The vast, 832-square-mile body of water is Ethiopia's largest lake, and is packed with ecological, cultural and historical charm. It is situated in the highlands of Ethiopia’s second-largest region, Amhara administrative state.

Ecologically, Lake Tana is home to rare and endangered bird species such as the black-crowned crane and also hosts several migratory birds.

Lake Tana is also notable for being the headwaters of the Blue Nile river that flows westward before it merges with White Nile at Khartoum, Sudan’s Capital.

The Blue and White Nile are the two major tributaries of world’s longest river, the Nile. Along the way, the Nile is fed by numerous smaller streams before it flows northward into Egypt, but the Nile gets more than 80 percent of its water from Blue Nile. Describing the eminence of Lake Tana, the renowned adventurer and geophysicist Pasquale Scaturro said, “The riches of Egypt is a gift from Lake Tana.”

Now, the lake is a very different symbol — of the dire state of Ethiopia’s natural resources at a time when the country’s fast-growing population needs more of everything.

When first spotted in 2012, the massive water hyacinth blooms were first confined to areas covering about 77 square miles of the shallow water and shores of the lake around its western edges. Since then, the floating weed has grown rapidly, devouring large swatches of the surface of the lake. As a result, the average expanse of the lake in the western province of Dembiya has steadily shrunken, residents told state media.

According to experts who spoke to government media, the water hyacinth has grown nearly 100 percent from 2012 to about 155 square miles, though a relatively dry winter season in 2016 slowed its expansion.

The spread of this invasive alien species is the result of human activity around Lake Tana. According to a paper written by two academicians, the rapid growth of the pernicious weed is caused by the inflow of nutrient rich water from urban and agricultural runoff and products of industrial waste, threatening other Ethiopian lakes as well such as Lake Hawasa, and Lake Zeway.

Since 2015, UNESCO has recognized Lake Tana as a World Heritage site for its unique ecological biosphere reserve, due to NABU's efforts to secure this status as part of its conservation efforts in the region. UNESCO also recognizes the islands’ rich historical, cultural and religious significance with deep ties to the Ethiopian Coptic Orthodox Church.

The lake is also home to historical monasteries and churches. Their relatively isolated location on islands has aided their preservation, but as the menacing water hyacinth threatens to clog the entire lake, their survival is at stake as well as the livelihoods of all who live near and depend on Lake Tana as a natural resource.