Emmanuel Bizimana lives on Rusogo, one of the hills that surround Karago, a small lake located in Nyabihu District. He knows the lake at its original size, before it started to dry up.

"I was born here, and I remember in the early 2000s, the waters used to reach the foothills and there used to be plenty of fish," says 42-year-old Bizimana, a farmer.

"By around 2010, the lake had begun to dry up due to muddy waters from the hills of Gishwati and Jenda sectors."

Lake Karago has a surface of 27 hectares, and six metres of depth. Grass has already grown on the banks of the lake. Bizimana reckons the lake will soon become a swamp unless something is done.

It is not the first time an appeal has been made to save the endangered lake. 

In 2011, a report by the United Nations Environment Programme (UNEP) indicated that Lake Karago’s water surface had shrunk by a quarter due to sedimentation. 

Another 2012 study by Rwanda Environmental Management Authority (REMA) found that 2,000-3,000 tons of sediment deposited in the lake annually.

In 2012, the Ministry of Natural Resources called for tree planting and land terracing as an erosion-control measure to save the lake.

"The trees have been planted on a 50-metre wide buffer from the water, but sediment from Gishwati stubbornly continues to deposit on the bottom of the lake,” says Jean Bosco Ntakiyimana, 40, who lives near the lake.

During rainy seasons, Nyamukongoro, a muddy tributary from Gishwati forest, flows through un-terraced hills, taking with it eroded soils into the lake, hence the siltation.

The government has set up a monitoring station at the lake to better understand what’s going on with its waters.

"We are monitoring the amount of water in Lake Karago to ascertain the level of its drying up,” said Davis Bugingo, head of flood management and water storage development at Rwanda Water Resources Board.

"However, the tests we have taken so far show that the drainage is still in normal range; basically, it has not yet reached an alarming stage.

Lake Karago is like other small lakes in Rwanda such as Ihema, Sake and Nasho in the Eastern Province whose water levels drop depending on the season of the year or environmental factors, Bugingo said.

The mountainous Nyabihu district is located in Rwanda's coldest northwestern region, where rainfall can reach 1,500-1,700mm in a year. Temperature can reach a minimum of 10 degrees Celsius.

Potential for fishing

Fishing in Lake Karago has been practiced for decades on a minimal scale, but local fishers say the location of the lake threatens some types of fish.

"Tilapia were introduced some years ago, but they could not survive in cold waters with a lot of sediment,” says Venuste Kayumba, the president of a fishing cooperative at the lake.

The cooperative can catch 600 tons of fish in a year, but Kayumba says they could get much more with an adaptive type of fish, called carp, which survives at low temperatures.

Carp were introduced in Nyirakigugu, a nearby lake of 10 hectares, when tilapia died en masse. Today fishers say they catch 400 tons of fish annually.

Local authorities say they too are concerned about the lake.

"With the help of different stakeholders, we are planning to plant trees along the banks of Nyamukongoro, among other measures to control erosion,” Antoinette Mukandayisenga, the Mayor of Nyabihu District, said.

She added that the district is working with the fishers’ cooperative to see how they could introduce adaptive fish into the lake.

Besides an economic loss, the drying up of Lake Karago also threatens biodiversity in the region.