Years ago I learned that the Columbia ice field was North America's triple divide point: water flowing from this ice field could drain into the Artic, the Pacific, and the Atlantic Ocean. Something I never questioned. Today I came upon this map, and was surprised to see that the triple point was actually further south, close to the USA/Canada border:

Major continental divides

I looked it up and found about Triple Divide Peak. The article has another, more precise map:

A map of North American drainage basins/divides

So it appears that there are actually two triple points. That led me to search which ocean Hudson Bay belongs to... and this is where it gets tricky. Citing various sources, Wikipedia says:

Hudson Bay is often considered part of the Arctic Ocean; the International Hydrographic Organization, in its 2002 working draft of Limits of Oceans and Seas defined the Hudson Bay, with its outlet extending from 62.5 to 66.5 degrees north (just a few miles south of the Arctic Circle) as being part of the Arctic Ocean, specifically "Arctic Ocean Subdivision 9.11." Other authorities include it in the Atlantic, in part because of its greater water budget connection with that ocean.

Some sources describe Hudson Bay as a marginal sea of the Atlantic Ocean, or the Arctic Ocean.

So, my questions are: Which objective criterion could be used to settle this dispute? Considering this criterion, which ocean Hudson Bay belongs to?

  • $\begingroup$ Unless there has been a ruling on it by an internationally recognised authority, which I doubt, you won't get a hard and fast answer, only an opinion. It's like the question of which is the longest river; there are several contenders. The Nile is generally considered the winner, but no one has ever made an internationally recognised decision on the matter. $\endgroup$ Commented Feb 4, 2020 at 14:12
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    $\begingroup$ It's not really like the longest river question, because that does have a clear, defined, answer (subject to choice of route). But otherwise Michael is right - apart from the IHO answer that you quoted, I suspect you won't get a clear answer, because whether it's useful to consider it one way or the other will depend on one's purpose at the time. From some perspectives the world only has one ocean... $\endgroup$ Commented Feb 4, 2020 at 14:15
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    $\begingroup$ My problem with the quoted paragraph is that IHO says one thing, but we don't know which argument supports it, and "other authorities" (we don't know which) say another thing, this time with an argument (water budget). So I was curious to hear from people familiar with the topic. Is the water budget argument a good one? If not, what other arguments could be used to determine which ocean the bay belongs to? $\endgroup$ Commented Feb 4, 2020 at 16:11
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    $\begingroup$ @Semidiurnal Simon: Even the "longest river" question is just a matter of opinion. IIRC that might be the Mississippi-Missouri river, but popular opinion is that the Missouri is a different river, putting the "source" in Minnesota rather than Montana. $\endgroup$
    – jamesqf
    Commented Feb 4, 2020 at 20:26
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    $\begingroup$ It's more of an "Is Pluto a planet" question. $\endgroup$ Commented Feb 28, 2020 at 6:01

1 Answer 1


Water above the blue line flows to the arctic. No question there. Water below the green line flows to the Atlantic. Also no debate.

Water between the blue and green lines flows to Hudson Bay. But where does Hudson Bay flow? The answer, technically, is both. But which one does it primarily flow to? From this article, it seems like the vast majority of flow out of Hudson Bay is to the Atlantic. In fact, it's an enormous source of freshwater to the Atlantic. A lot of that water comes from the Arctic Ocean (and here is where the definition of 'ocean' becomes itself kind of fraught).

But if you were to simply ask: "at which point in the continental US would water FLOW to three different oceans?", Snow Dome has the better claim. The majority of water leaving the Montana Peak towards Hudson Bay will end up in the Atlantic Ocean, not the Arctic.

If you were to ask, "at which point(s) does any water flow to all three Oceans?", it's technically the entire locus of points along the great divide between these two "triple points".

But if you had to pick just one point, Snow Dome seems more appropriate.

  • $\begingroup$ Thank you for the reference, it helped me find this peer-reviewed article which has some nice information about water in/out-flows between the Hudson Bay and both oceans. $\endgroup$ Commented Mar 7, 2022 at 9:27

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