Passage: Gabon's largest river is the Ogooué which is 1,200 kilometres (750 mi) long. Gabon has three karst areas where there are hundreds of caves located in the dolomite and limestone rocks. Some of the caves include Grotte du Lastoursville, Grotte du Lebamba, Grotte du Bongolo, and Grotte du Kessipougou. Many caves have not been explored yet. A National Geographic Expedition visited the caves in the summer of 2008 to document them.Gabon is also noted for efforts to preserve the natural environment. In 2002, President Omar Bongo Ondimba designated roughly 10% of the nation's territory to be part of its national park system (with 13 parks in total), one of the largest proportions of nature parkland in the world. The National Agency for National Parks manages Gabon's national park system.

Question: How long is the Ogooue river?
1,200 kilometres (750 mi)