Complex sentence: The Asón is a river in Northern Spain, flowing through the Autonomous Community of Cantabria and flows into the Cantabrian Sea in the town of Colindres, where it forms the Santoña estuary which is the most important SPA in the north of Spain.
Split into simpler sentences: The Asón is a river in Northern Spain, flowing through the Autonomous Community of Cantabria. It flows into the Cantabrian Sea in the town of Colindres, where it forms the Santoña estuary which is the most important SPA in the north of Spain.