Castle Semple Loch is a large freshwater loch located in Renfrewshire, Scotland. It is part of the Castle Semple Country Park, which offers various outdoor activities such as walking, cycling, and birdwatching. The loch is popular for sailing and other water sports, attracting both locals and visitors. The loch is surrounded by scenic landscapes and rich wildlife, making it a great spot for nature enthusiasts. It is also home to several species of birds, including swans and ducks. The area has historical significance, with remnants of the Castle Semple estate nearby, adding to its charm.