All aboard! At one and the same time, the Bellman delivers himself from an impending watery grave, snatches a coveted berth aboard the H.M.S. Snark, tingles his bell to signal our departure and introduces the Beaver, who is busily engaged upon her salubrious lace-making.
I am aware that readers assume the Beaver to be a He. Carroll's text is ambiguous on the point, only using the masculine (possessive) pronoun in the plural to refer to the Beaver and another (usually the Butcher). In his Annotated Snark, Martin Gardner concurs on this important grammatical point, which is reinforced in my mind by its aesthetic rightness.
Inasmuch as the Snark is an imaginary animal and thus its clochetic pursuer triply so, and inasmuch as beavers are usually riparian, sedentary and unimaginably disinterested in travel and the needletrade, be it resolved:
No Bellman can step into the same river twice, for there is no Bellman, nor any river (or else he could step into it twice) and hence, all other passengers of any vessels upon these waters are also unreal, or at least up for some ontological gender-bending.
QED, the Beaver's a She and not a He and any arguments to the contrary are futile, for nothing will come of nothing. Speak again of this matter and I will invoke my Aristotelian rights: nature abhors a void, especially a kingly third portion (AKA the artists' Law of Thirds). Now stop learing at this nice drawing and get busy googling Heraclitus and Shakespeare, the bookends of occidental thinkery.