About the Susquehanna River -- Follow the links to dive deeper.
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The Susquehanna River is one of the oldest existing rivers in the world, being dated at 320–340 million years old. The ancient channel is still recognizable on navigation charts and can be traced all the way to the mouth of the Bay and on out to the great fishing canyons at the edge of the continental shelf.
The Susquehanna is 444 miles long. It's source is at Otsego Lake near Cooperstown, NY. It's mouth is at Havre de Grace, MD. Draw a line from Concord Point Light across the river to the old stone mill in Perryville, and you are at the end or, navigationally speaking, the beginning of the river... Mile 444 or MIle 0 depending on how you look at it.
There are two main branches of the river. The main branch or "North Branch" which begins at Otsego Lake and the "West Branch" which begins at near Elmora, Pennsylvania in northern Cambria County. Some folks along the West Branch take exception to the North Branch being referred to as the Main Branch. Take a virtual tour.
At the height of the last ice age, about 20,000 years ago, the river extended all the way out to the canyons on the continental shelf. There was no Chesapeake Bay then. As the earth began to warm (naturally) the ice caps and glaciers began to melt and raise sea levels. By about 8,000 years ago the sea levels and land subsidence gave us the present form of the Chesapeake Bay estuary.
The Susquehanna is only "navigable" to Port Deposit, just a few miles upstream of the "fall line." From Port Deposit upstream, the river is shallow but wide and often rocky. Downstream of Port Deposit, the river becomes part of the Chesapeake estuary.
There are four major hydro-electric dams on the Susquehanna: Conowingo, Holtwood, Safe Harbor, and York Haven. In addition there are numerous smaller "low-head" dams up and down the river. The large dams, like the Conowingo, also serve as sediment and debris basins. But they are quickly filling resulting significant environmental issues downstream.
The Susquehanna Flats at Havre de Grace was formed where the river current diminishes and drops its sediment load. This has created a broad, shallow "head" of the bay where submerged aquatic vegetaion (SAV) has regained dominance. These grass beds, while annoying to boaters, are critical to the aquatic/marine life diversity of the upper bay.
There are many excellent sources of information about the Susquehanna River. Here are a few links:
Susquehanna River Basin Commission
Source: Chesapeake Quarterly
Otsego Lake, Cooperstown, NY
Susquehanna West and North Branches
Source: Dr. Ron Blakey, Paleogeography and Geologic History of North America
Source: Brittanica.Com https://www.britannica.com/science/fall-line
Take a GoogleEarth flyover of the Susquehanna River from its source in Otsego Lake at Cooperstown, NY to Port Deposit in the YouTube video to the right
After starting video, place cursor over the video window and type "f" to view in fullscreen