Complex sentence: Prospect Point (a spit of land that points at Duck Island) protects a small area of water from high winds that used to be (since before 1940) a popular spot for model boats; though model boating is no longer allowed on the lake.
Split into simpler sentences: Prospect Point (a spit of land that points at Duck Island) protects a small area of water from high winds. This used to be a popular spot for model boats, though model boating is no longer allowed on the lake.