What is the primary role of the power plant stacks near Oswego Harbor?

The primary role of the power plant stacks near Oswego Harbor is to serve as navigation aids. These stacks are tall structures that help pilots and mariners identify their location in relation to the harbor and surrounding areas. The visibility of these stacks from a distance can assist in navigation, providing a point of reference for boats and ships as they approach the harbor.

The other options, while possible roles for some structures, do not accurately reflect the function of the power plant stacks in this specific context. For instance, the stacks do not provide energy to local communities directly; that is a function of the power plant itself. They are not designed for fishing or recreational activities, which would require different types of facilities that are more focused on those purposes. Overall, the stacks' design and strategic placement make them primarily useful for navigation.