There are three lakes in Africa with a major problem. Their names are Nyos, Monoun, and Kivu. Volcanic activity beneath these lakes cranks them full of carbon dioxide, which builds to ludicrious pressure. This changes them, over time, from an ordinary lake into a can of violently shaken soda. At some point, a trigger sets them off into a huge explosion of water and carbon dioxide, which floods everything nearby and suffocates all animal life to death in a massive cloud of CO2.
French environmental scientists have installed a solution in Nyos in which they deliberately set off the eruption...inside a tiny pipe. This small eruption is cleaned up by local trees before any human sees it, and effectively is a self-perpetuating fountain. The lake's own CO2 shoves the water up the pipe, over and over and over, and this usage makes it impossible to build up to explosive levels. The villagers that live nearby can sleep peacefully.
Now, this fountain is pretty, but it's pretty sane science. Also, it is reported that to truly prevent eruption, we need five more of them. Maybe ten. So, I have a much much crazier solution.
We deliberately eutrophize the lake by adding iron and phosphorus, and extract the resulting plants for fertilizer and/or animal feed. Oxygen tends to bubble out of the lake rather than build up until it explodes, and the resulting muck is economically useful. This would be a continuously available resource, as we can recycle the phosphorous and iron from cheap sources. In phosphorous's case, sewage. Iron can be taken from rusted machinery beyond its useful life. This also sinks a large amount of carbon into animal life. Namely, whatever animals survive long enough to consume the algae. They may have to be manually reintroduced -- the natural state of the lake probably killed off any naturally present animals with carbonic acid.
On the downside, I think that much algae together may smell strange.