I know there are longer un-dammed rivers open to the ocean in Alaska and British Columbia. I also know there are longer un-dammed rivers in the contiguous 48 United States, but they are not open to the ocean (e.g. the Yellowstone, which joins the Missouri, which is dammed). The Delaware River has no dams on the 330 mile long mainstem, and opens to the Atlantic Ocean.
I had always heard that the Edisto was the longest undammed river that flows into the Atlantic, but maybe that's just in the southeast---not sure if it's longer than the Delaware.
I don't suppose the lower Mississippi counts. Are you looking for a watershed that is entirely undammed?
Rich, the Altamaha River is know to be among the longest undammed in the east, but I think it is only about 220 km....
Readers are directed to Georgia Encyclopedia for the combined Ocmulgee River stated below Lloyd Shoals/ Lake Jackson Dam (GA Power) as 241 miles where joins the Oconee River to form the Altamaha River to the sea at 130 miles or a total of 371 miles. Please double check.
Douglas Burns - According to several sources (e.g. www.americanrivers.org/river/edisto-river/ ; www.edistofriends.org/edisto-river; wikipedia) the Edisto River is 250 mi. long, so 80 mi. shorter than the Delaware. Ideally it'd be nice to have a more definitive source, like the USGS, to cite for river info. like this.
John Garver - Thanks for mentioning the Lower Mississippi River. Nothing in my question disqualifies it, and at ~ 1,000 miles, it's much longer than the Delaware River. So I can't claim that the Delaware River is the longest undammed river open to the ocean in the lower 48 United States. Having said that, the Lower Mississippi River is so disconnected from its floodplain and upper river, and so polluted, it's not comparable to the Delaware River (or the Edisto or Altamaha Rivers).
Frederick Marland - Thanks for your answer! As far as I can tell you are correct, with one small caveat. There is a hydropower dam across the Ocmulgee River at Juliette, GA, which blocks the migration of American shad upriver. This dam is roughly 20 miles downstream of the Lake Jackson Dam (using road miles as a estimate for river miles). Subtracting this length leaves about 220 miles + 130 miles = ~350 miles of river open to the ocean; more than the Delaware River! The hydroelectric facility at Juliette has been shutdown by FERC, but the dam remains. If the dam is removed, it'll restore an additional ~ 20 miles of river for American shad.
I'd guess I'd note that the Penobscot River in Maine is an up and comer on this list with several key dam removal projects now completed (Veazie and Great Works dams) and a free bypass channel around the Howland Dam. If its fish passage you are after, this one is a new contender, but I am uncertain of the total length (in this case the main stem and then West branch). .
Yes, it's largely free, open passage for diadromous fish that I'm interested in. The progress made opening the Penobscot to migratory fish is amazing and inspiring! However, it's a shorter river than the Delaware, so isn't a contender as far as length goes.
Richard Evans;
In 2014 my understanding was that obstruction at Juliette Shoals on the Ocumulgee was scheduled to be removed. Thanks for your thoughts. I will check further on that point. fred
The Ganges river in India doesn't have any dam on the main river (of course there are many on its tributaries). It is almost 2525 km.
Wow. Thanks, but my question was about rivers within the contiguous 48 United States.
Douglas A. Burns , Jonathan G. Kennen , John I Garver , Frederick Marland, Ph.D. , Dipteek Parmar , Kelly O Maloney , Tanja N Williamson , Stefanie Alexa Kroll , Karen Riva-Murray , John A. Young , Matthew R. Marshall , David M Lodge
It's now been more than two years since I posted this question. The answers received point out there are some details involved that I didn't specify in my question. I should have specified that I was limiting this to (a) rivers that do not have any dams on their mainstem, and (b) the length of the mainstem of the river, not including branches or major tributaries. Criterion (a) "disqualifies" the the lower Mississippi River (which has ~ 1,000 miles is open to the ocean). Criterion (b) "disqualifies" the Altamaha- Ocmulgee system as a contender. Btw, if I included the East Branch of the Delaware River, which is ~33 miles long from the mainstem upstream to the Pepacton Reservoir Dam, the total length would be 363 miles - longer than the Altamaha- Ocmulgee system.
What I was really interested in was finding the longest mainstem river that had no dams and was open to the ocean and supported diadromous fishes. By those criteria, I conclude and assert (until someone proves me wrong) that the Delaware River is the longest mainstem river open to the ocean supporting diadromous fishes in the lower 48 United States! Any challengers?
This may be a useful paper to help resolve. In particular, check out Fig. 9. It looks as though the Ogeechee River in GA may be the longest that fits your criteria. I'm not sure why the Delaware is not mentioned, but perhaps it has/had lowhead dams on it somewhere that were since removed? In any case the rivers noted on Fig. 9 provide a solid collection of the high quality rivers that would likely support diadromous and anadromous fishes.
https://www.jstor.org/stable/pdf/1467936.pdf?casa_token=_EstSirVd7gAAAAA:NkK7ZNH24lWllpBWHxO-N58fvFEMEQ8E9vAaNzRFoYQdyiKX0Zx--rWygRJhhTC_7JGf3O18NT9aZF5-MjfCB9wg9fYnYThrr_qI27GBGZ0fdxJ7YNZ1
Richard A. Evans I'm not sure that the Delaware qualifies. There is a low head dam in Easton, PA. You can find pictures of this on line. Can fish easily migrate up over this dam? There also appears to be one or more wing dams, but since these have a central opening, they would seem to meet your condition of allowing fish passage. Therefore, the Ogeechee River, GA might be the winner. I was promoting the Edisto earlier, which has no dams along its 250-mile length.
Andrew L. Rypel , Douglas A. Burns Thank you for your responses! My bold challenge got some attention and good information! This has been an interesting exploration of free-flowing rivers and I've learned from it!
I admit I'd like to champion the Delaware River because 3/4 of the non-tidal Delaware River is designated "Scenic and Recreational" under the Wild & Scenic Rivers Act, administered by the National Park Service for which I work, and it has very good populations of diadromous fishes that freely migrate through the entire mainstem.
However, I also have to admit there are some low-head dams on it, and several major dams/reservoirs on major tributaries that compromise it's "free-flowing" quality. So I have to rescind my bold claim. But that's o.k. It's still a great river that deserves more appreciation. Some of that seems to be coming: American Rivers just designated the Delaware River the River of the Year!
How about on the west coast? I live in Washington on the South fork of Skykomish River which flows into the main Skykomish and eventually joins the Snoqualmie River, which has several dams, to become the Snohomish River until it hits the Salish Sea in Possession Sound.
Adam wicks-arshack The Skykomish River doesn't qualify by the criteria I've set: The mainstem of a river open to the ocean (open to migratory fish) that does not have any dams on it. As you state in your answer, the Skykomish River is a tributary, not a mainstem river, and it "eventually joins the Snoqualmie River, which has several dams." The dams on the Snoqualmie River disqualify it.
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