Lake Suwa
, also Ito Shizu Sen (糸静線) is a major fault on Honshu island that runs from the city of Itoigawa, Niigata Prefecture, through Lake Suwa to the city of Shizuoka in Shizuoka Prefecture. It is often confused with the Fossa Magna (Great Fissure Zone), a geological feature it forms the western boundary of.