I meant to write this column last week but went down a John Wesley Powell rabbit hole instead. My plan had been to examine illogical, multiple-outlet watersheds draining into separate oceans, but I critiqued right-angled state boundaries instead.
I’ll give it another try this week. Hopefully, I won’t get distracted this time.
A new scientific paper published in April in the journal “Water Resources Research” explores bifurcated rivers in the Americas. There are certainly examples in the Old World as well, but this paper just covers the Americas.
Bifurcation is a fancy word for a river that forks or splits around an obstacle such as an island. The paper examines a special kind of bifurcation, however; a bifurcation that peels off the main stem of a river but never returns.
There are echoes of ancient bifurcation all around us. During the glacial period of the ice age — we’re in an interglacial period at the moment — ice dams in mountain saddles sometimes allowed fish to migrate into new watersheds previously unavailable. Westslope cutthroat trout may have found their way east of the divide through such a process and Marias Pass may have been a place where this occurred.
Marias Pass isn’t on the list since it has returned to its separate watersheds in the interglacial period. Bear Creek flows west from the pass and the South Fork Two Medicine River flows east.
A few east–west bifurcations still exist in the Rockies, however, and North Two Ocean Creek in Wyoming’s Bridger-Teton National Forest may be the most famous. The creek emerges from a steep canyon into a broad saddle where an alluvial fan splits the flow east and west. The eastern drainage is Atlantic Creek, which empties into Yellowstone Lake, then the Yellowstone River, and eventually, the Gulf of Mexico.
The other side of the Y, Pacific Creek, joins the Snake River, and I think you can guess which ocean it joins after that.
North Two Ocean Creek may have played a role in the unfortunate introduction of lake trout into Yellowstone Lake. That introduction, long thought to be the result of bucket biologists spreading their favorite fish around, might instead be the result of lake trout moving upstream from the Snake River into Pacific Creek, then hitching a ride on Atlantic Creek down to Yellowstone Lake.
The most likely suspect remains bucket biologists, but the “Two Ocean Pass’ theory hasn’t been ruled out.
Lake trout in Yellowstone Lake have had grave consequences for Yellowstone National Park’s aquatic ecosystems. The lake’s native Yellowstone cutthroat trout spawn in the spring in tributary streams around the lake and those spawning cutties are an important food source for hungry grizzlies fresh off hibernation.
Lake trout are a double whammy on the balance of life in the Park. Those big lakers not only eat lots of Yellowstone cutties, stealing meals from the griz, but they also spawn deep in the lake, so they’re rarely available for griz or the lake’s avian predators of surface-feeding fish.
Two other divide splitting bifurcations in the Rockies are the aptly named Divide Creek, and the Committee’s Punch Bowl.
Divide Creek is west of Calgary on the continental divide, which forms the border between British Columbia and Alberta. Like North Two Ocean Creek, Divide Creek splits at a high saddle. The flows to the west eventually join the Columbia River. The water flowing east becomes the Bow River, one of Canada’s greatest trout streams.
The water of the Bow eventually finds Hudson Bay.
The Committee’s Punch Bowl, named after a managing committee of the Hudson Bay Company, is a small lake also on the divide, a bit north of Divide Creek. The lake has two outlets, the Whirlpool River which flows north, eventually joining the Mackenzie River and ultimately, the Arctic Ocean.
The southern drain is another Pacific Creek, this one a tributary of the Columbia River.