To prevent this, several vertical pipes are installed in the lake. Cold, gassy water from the bottom of the lake flows up the pipe. Bubbles form and grow as the pressure drops, and a mixture of water and gas froths out the top. However, the pipes require maintenance, and the ability to remove carbon dioxide is limited by the flow rate.
Pressure reduction is one cheap and effective way to remove carbon dioxide from water. Another way is to create nucleation sites for carbon dioxide bubbles to form. Many years ago, there was a fad where people would drop a Mentos candy into a bottle of Diet Coke. The rough surface of the candy contained many small air pockets. It is far easier for an existing bubble to grow than for a new bubble to form spontaneously, so bubbles would rapidly grow and break away from each bit of roughness on the candy.
We could do something similar with Lake Nyos. Instead of Mentos, we'd sprinkle the lake surface with silica gel powder (basically, sand etched with acid to create trillions of tiny pores), or titanium dioxide (used in paint and icing). The particles would slowly sink, with a frothy column of bubbles rising above each. We'd only add a small amount at a time, so the people living in the region wouldn't be suffocated by a lethal amount of carbon dioxide froth. As the powder sank into the mud at the bottom and the frothing stopped, we'd sprinkle on some more. We'd definitely want to wear SCUBA gear as we shoveled the powder from our boat onto the water, so we wouldn't be overcome by the fumes.
After a few months of adding powder, the lake would no longer be saturated with carbon dioxide. We'd still go out occasionally and drop in some more powder, just to keep the levels from rising again.
Any other suggestions for degassing Lake Nyos?