Agusan (ägōˈsän) [key], river, c.240 mi (390 km) long, rising in the mountains of SE Mindanao, the Philippines, and flowing N past Butuan to Butuan Bay. It is navigable for small craft c.160 mi (260 km) upstream. The Agusan valley is very fertile and is one of the chief rice-growing regions of the Philippines.
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