One of the oddest of cryptids is an octopus haunting the lakes of Oklahoma, a landlocked state. The reason this is odd is that although freshwater mollusks are common, Cephalopoda (the class consisting of nautiloids, ammonites, belemnites, octopus, squid and cuttlefish) is exclusively marine. The chemistry between fresh and salt water has so little compatibility that few animals manage to cross between both (among those few being salmon, bull sharks, saltwater crocodiles and ancient ambulocetids).

For a cephalopod to transition from salt to brackish/fresh requires certain changes in its physiology. Could such a change be possible, or is a freshwater octopus as likely as an elephant-sized terrasquid?

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    $\begingroup$ Is there any reason why they shouldn't be able to? Few animals do manage it, but is that because of the difficulty or because of the lack of a need? If there's an evolutionary reason why an octopus would need to go between fresh and salt water, then I don't see any particular reason that an octopus couldn't evolve to do so - however I'm no marine biologist so I shan't claim to be able to provide a definitive answer. $\endgroup$ Jan 5, 2017 at 19:21
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    $\begingroup$ How would a saltwater octopus get to Oklahoma? $\endgroup$
    – CHEESE
    Jan 5, 2017 at 19:28
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    $\begingroup$ Being a native of Oklahoma, I can offer a very real-world answer: people release wild animals into our lakes and parks all the time. It's not so different from people flushing baby gators down the toilets, or introducing things like the snakehead into the waterways. I don't know the science necessary to making this plausible, but it wouldn't surprise me - at all - if people had octopi or squids in aquariums, and either got tired of them, or just got bored, and released them into local waterways. You might roll your eyes, but you vastly underestimate Oklahoma if you do. $\endgroup$ Oct 21, 2018 at 19:15
  • $\begingroup$ @CHEESE -- He'd take Route 66, of course! It winds from Chicago to LA, doncha know? $\endgroup$
    – elemtilas
    May 14, 2019 at 21:59

2 Answers 2


Picture a lake directly connected to the Ocean or rather an inland sea. It has some flow of fresh water into it from rivers, but it's large and because of it's connection to the Ocean the salt content is about the same or probably a bit lesser as the Ocean.

Now picture a major geologic event that raises the elevation of the lake, and leaves a river outlet to the sea. Now you have a large salt water lake. Its outflow is larger than what is lost to evaporation, but combined the water lost to both is matched by rainfall and rivers flowing into the new lake.

Now, assume that the slow desalination as fresh water replaces the outgoing salt water will take some thousands of years to completely take place.

Such a slow rate of change could give opportunity for the generations of octopus to steadily become more tolerant of the less salty water until they are fresh water octopus.

Whether it would happen is another question.

  • $\begingroup$ Great understanding of evolutionary pressures and gradual change. $\endgroup$
    – XenoDwarf
    May 15, 2019 at 1:19

Cephalopods don't have a sodium pump in their gills in the way arthropods and fish do. Their "kidney"(nephridium) handles all osmotic balancing, which is fine in the ocean but makes it nearly impossible for a transition to freshwater. They will start taking on water and losing salt to the environment and lack a way to reclaim it easily. It is understood that freshwater clams and snails get around the problem by being very small and compact but even then they have some of the lowest body salinity levels in the animal kingdom. More research needs to be done.

There is speculation that the presence of a shell helps buffer snails and clams during their transition by acting as an osmotic barrier and, possibly, an ammonia sink.

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    $\begingroup$ Now this is an answer. Cepahlopods would need to evolve a sodium pump. $\endgroup$
    – a4android
    Jan 6, 2017 at 0:58
  • $\begingroup$ @a4android That answer needed grammatical polishing. $\endgroup$ Jan 6, 2017 at 1:37
  • $\begingroup$ @JohnWDailey It has had some polishing. :) $\endgroup$
    – a4android
    Jan 6, 2017 at 2:56
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    $\begingroup$ So it was easier for molluscs to conquer dry land than fresh water? There are some decent sized land snails and slugs. What defences do large slugs have against heavy rain, in which weather they thrive? $\endgroup$
    – nigel222
    Jan 9, 2017 at 12:47
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    $\begingroup$ rain is not emersion, the osmotic effects of rain are minimal becasue they are not breathing it. You can actually drown land snails. Most of their body (like most animals) is watertight and an osmotic barrier, gills however can't be if they work as gills. Air on the other hand only has a mild drying effect which they already have to deal with because saltwater has the same effect. Osmotically living on land and living in the ocean are much more similar to each other than freshwater. $\endgroup$
    – John
    Jan 10, 2017 at 5:17

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