Gin and tonic in hand, I sat at a local Kisumu haunt, looking out over the vast expanse of Africa’s largest freshwater lake. The waters typically reflect a bright blue equatorial sky, beneath which hippos, crocodiles, and the world’s highest concentration of cichlids — those bright tropical fish popular in doctors’ office aquariums the world over — have flourished for centuries.

To call this place by its staid colonial name, Lake Victoria, seems all wrong. Lowle, the local handle, meaning “vast and unending,” is far more appropriate for a lake that covers 26,000 square miles. Native lore places the origins of mankind in Lowle’s depths, and science seems to have at least partly confirmed this. The Leakeys, those iconic British archeologists, made their first notable discovery, a 25-million-year-old skull of a creature that later evolved into both man and ape, on an island in the lake. Lowle is also the source of the river Nile, which helped to nourish the fertile valley where so much of modern civilization began.

But as we sipped our drinks, the view calming our thoughts and throwing each of us into a kind of quiet solitude, we saw no water. Not an inch of blue. Water hyacinth, a glossy, invasive plant species had turned the tranquil lake into a field of green. The winds would eventually blow them to another part of the lake, but the hyacinth had already lingered for months. Acquaintances, some of whom had lived in Kisumu, a lakeside town in western Kenya, for decades called it the worst invasion they’d ever seen.

The hyacinth was so lush that it brought with it a forbidding sense of permanence. Other weeds and grasses were taking root on top of the hyacinth. With shrubs of differing heights, delicate purple flowers, and gently rolling greenery, the expanse looked rather like a prairie. It was beautiful, in its own way, but as I soon learned, it spelled disaster for the lake.

When the hyacinth blows ashore, it blocks boats and quashes local fishing, a lifeblood industry in one of sub-Saharan Africa’s most populous regions. The plant chokes off ports, commerce, and transportation, bleeding the nearby towns of millions of dollars. Underwater, the hyacinth is even more destructive. The weeds block sunlight and de-oxygenate the lake. Malarial mosquitoes gain a stagnant place to breed and tiny snails carrying bilharzia (that parasitic worm that infects so many lakeside children) proliferate. Scientists call the toxic environment created by water hyacinth a “dead zone.”

The species evolved in the Amazon, where competing flora keep it in check. But when it found its way to Lowle, likely jumping from some expatriate’s ornamental pond and floating down the river Kagera before finally spilling into the lake, this invasive weed found a bounty of nutrients to feed its exponential growth and an absence of insect predators to curb its flourishing. Doubling in size every two weeks, the hyacinth has proved, thus far, impossible to root out.

I wanted to talk to people who made their living on the lake about how the hyacinth invasion was affecting them. My questions brought me to Nyakech, a small fishing town an hour’s drive down good roads from the big city of Kisumu. My guide was Tom, a local legend with an encyclopedic knowledge of the lake. The concrete roads eventually turned to dirt and then ebbed into a simple footpath as I followed him toward the lake.

The shore was dotted with mangroves and grassy outcroppings of reeds, and there were clusters of fishermen paying no mind to exotic cranes and egrets, the height of small children, posted like regal sentries over the blue waters. Yes, blue. We were astounded to find that the hyacinth, which had lingered in Nyakech for months, had cleared away by the time we arrived, the decaying boats, once trapped by the hyacinth, the only remnants of the invasion.

The fishermen we found, Peter and Jacob, were in high spirits, going about the business of detangling hundreds of meters of net. They each stood ankle deep in water, their strong bodies and straight backs contrasting with other signals of their age, the grey hair around Peter’s temples, the crows feet extending from Jacob’s eyes. They were fisherman of the old school, who saved their money instead of drinking it away in times of plenty and had worked the lake for decades. They were just the people to talk to.

Two weeks prior, they said, we would have found them in quite a different state. The hyacinth had landlocked their boats for months, and they were barely scraping by. Those had been “hungry days,” they explained matter-of-factly. Their children had to be pulled from school because they could not pay the fees. But on that sun-drenched morning, at the tail end of the dry season, with the hyacinth blown away and the buzz of fishing activities resuming, we found them in a more celebratory mood, happy to chat.

With a half century of fishing between them, the fishermen agreed they had never seen anything like the hyacinth before it started appearing on the lake in the mid-1990s. They called it amosi, a greeting in the local Luo dialect, a fitting description of a plant whose leaves spread out like a waving hand. But they soon received word from other lake fishermen that amosi would be their undoing, that it was a “ghost” come to destroy them.

At first the water hyacinth was simply a menace, something to push aside before they set out to fish in the mornings. Then the men started losing their nets in the mess as it spread and thickened. The loss of nets, costing up to $350 a pop, amounted to serious financial strain on the fishermen, who pull in a few dollars of profits a day. Fishing boats fell victim to the hyacinth, too. Surrounded and trapped by the weeds on the decaying shoreline, they rotted and became useless.

But the fishermen fought back. At first they tried to remove the hyacinth by hand, laying it in heaps at the shore and then burning it to kill the stench. But their manual removal proved no match for the rapidly multiplying weed, which would replenish itself overnight. Then, like so many who depend for their livelihood on forces beyond their control, Peter and Jacob started praying. They prayed every Sunday in their tin-roofed churches, swaying, eyes-closed, to the drum and organ music for the ghost to vanish.

The hyacinth remained. Their prayers unanswered, Peter and Jacob turned to traditional methods, pooling their money and employing a jabilo from neighboring Tanzania, a place believed to have the most powerful medicine men. He took their money. He promised to conjure powerful winds that would carry the menace permanently away. Then, he himself went permanently away, leaving them frustrated, aggrieved, and poorer.

The fishermen I spoke to had also heard tell of other schemes to remove the scourge. Some had introduced beetles to prey on the hyacinth patches. But the hyacinth won the battle, and now the beetles remain, flocking to the lakeside at dusk, an irritating reminder of failure. Others had employed industrial shredder boats, an effort costing millions, which chewed up the hyacinth for a time, but failed to ultimately solve the problem.

My guide told me of more recent proposals to remove the hyacinth and transform it into biofuel and fertilizer, plans to — as he put it so succinctly — turn the “devil into an angel.” But these efforts have yet to materialize.

Peter and Jacob keep praying the hyacinth won’t return, even though they know it will. The hyacinth have been woven, netlike, into the fabric of their difficult lives. Until December, the month when they expect to walk out to the water and see green instead of blue, they are getting on with the daily grind of fishing, their recent hardship making their task feel, for the time being, more providential opportunity than tedium.

Their teenaged sons, who held the netting aloft as their fathers untangled the knots, stayed silent during our talk. They worked quietly, absorbing the suppressed foreboding of our words, which provided no obvious redemption from their plight. They were working as their fathers and grandfathers had worked before them. They are the youngest laborers in a toilsome chain that stretches back to that first man to emerge from Lowle all those millennia ago.

At least for now. Tom, my guide, wondered if that could be changing. As we left the fishermen to their task, silhouetted by the sun-drenched lake, he said, “Those boys, know the hardships. They won’t become fishermen like their fathers.”

Kim Siegal is a writer and blogger who lives with her husband and two children in Kisumu, Kenya. You can find more at www.mamamzungu.com.