I once sat on the bottom in thirty feet of water and ate oysters. I was able to open them, put them in my mouth, expel the seawater and swallow them without the use of any tool or scuba equipment. I think our ancestors may have done that easily. Look at our hands-squared compared to the elongated hands of other primates. More paddle like, and between the fingers and toes, there is evidence of webbing.
Some people have more than others do.
There is no doubt that we are the swimming ape. We know how to move through water and our bodies seem to be designed for it. When you pour a pail of water onto a chimp or a monkey, the hair follicles on the body actually resist the flow of water, whereas on the human, the hair follicles flow with the water. When we pull our heads from the water, the water streams down and is diverted from the eyes by our eyebrows. This is a very functional use for this strange pattern of hair growth.