There are quite a few distinctions between humans and other apes that point indeed to a semi-aquatic evolutionary stage.
Hairlessness, subcutaneous fat, salinic tears are all traits of aquatic mammals which few land animals share.

I read that theory several decades ago, and one of the arguments they had was:
"just go to any body of water during a warm day and observe. What are most people doing?
Are they sitting in the trees, shaking down fruit, or are they walking on the shore, sifting through sand, wading, splashing and swimming?"
(Not exactly a scientific argument, but hilarious nontheless.)

There is also the interesting fact that of all animals, dolphins have the brain (and probably DNA structure) which closest resembles the human one.
Which is a relatively new discovery.
Funnily enough, there is also an ancient Greek legend that dolphins are magically transformed humans.
That's, like, 3000 years ahead of official science, ha.