Gersoppa Falls is formed by the river Sharavati.
Option 1: Lohit - Lohit river is not associated with the formation of Gersoppa Falls.
Option 2: Tungabhadra - Tungabhadra river is not associated with the formation of Gersoppa Falls.
Option 3: Sharavati - This is the correct answer. Gersoppa Falls is formed by the Sharavati river.
Option 4: Krishna - Krishna river is not associated with the formation of Gersoppa Falls.
Therefore, option 3 is correct - Gersoppa Falls is formed by the river Sharavati.