Rivers flow from mountains to seas or other bodies of water. A river's course is the route it takes from its source to its mouth. In the middle course, rivers form curves called meanderings. A river's flow is the amount of water it carries, which varies based on precipitation. Flow regime refers to whether the flow pattern is regular or irregular throughout the year. Watersheds are areas drained by rivers flowing into the same sea. Spain's rivers belong to three watersheds - Cantabrian, Mediterranean, and Atlantic.