The term "Finger Lakes" describes a group of lakes in the western part of upstate New York. They are a group of long, narrow lakes that roughly resemble fingers that lie south of Lake Ontario. They run mostly north-south and area among the deepest lakes in the US. The deepness of these lakes is the main clue to how they were formed; they were formed through glacial erosion. A glacier in the Pleistocene era moved southward and deepened a series of river channels. Debris left behind by the glacier caused the water to dam and the Finger Lakes were ultimately formed.