Lake Nyos, from Cameroun, released 80 million cubic meters of carbon dioxide gas in its surroundings with a speed of 50 kmph and suffocating everything within a 25 km radius. That is tough.
Since then the researchers have found several such lakes that erupt and all of them are in Africa. These lake eruptions are called limnic eruptions and they are deadly. Now the researchers have measurement devices all over lakes Nyos and Manoon and they also have built pipes to let that carbon dioxide get out and not bursts whenever it pleases to.
Lake Kivu, on the border of Rwanda and Congo seems to have the same accumulation of gases issue. Kivu has also pockets of methane in its belly and right now some of that methane is used to power some of the homes of the 2 million people living on its shores.