Pennsylvania's Natural Drainage System
More than ninety-three percent of Pennsylvania is drained by three river systems - the Delaware, Ohio and Susquehanna.
Pictured left is a wintry Allegheny River, which drains into the Ohio system in Pittsburgh.
Because of the river's lock and dam system, it is not uncommon for all of the sections north of Pittsburgh to freeze over, while the water at the Golden Triangle does not.