“Maybe you smell the coffee someone is drinking on the pier,” Ms. Cox told me. “There’s this awareness of the ripples of water, the pelicans sliding right by. Maybe your heart stops as you see a wave of silvery anchovies swimming below you.” In the hushed oceanic roar, you can choose to filter some things out and to focus on others.

Cognitive scientists have shown that water sounds — the rhythmic hum of the ocean, the rush of a waterfall — are calming to the human brain. We experience a drop in heart rate and blood pressure and an increase in alpha-wave activity — those brain wavelengths associated with relaxation and boosted serotonin — as well as creative thinking. While tooling around on the Spotify music-streaming service one day, I found that white-noise water sounds are some of the biggest hits there; a track called “Rolling Ocean Waves” has been played nearly 60 million times.

Walks in the woods are all well and good, as Thoreau illustrated in his transcendentalist classic, “Walden.” But during the two years, two months and two days that he spent living in that cabin at Walden Pond, he also got up early every morning to swim; he described it as “a religious exercise, and one of the best things which I did.” Each of his swims stimulated body and mind. Each day’s routine of rousing early to do so was a way to enact his desire to “live deliberately” in the New England forest.

Much has been made of the walk as the instrument for big thinkers: Charles Darwin; Albert Einstein; Amos Tversky and Daniel Kahneman, who famously rambled together and revolutionized our understanding of the psychology of decision-making. Less has been explicitly made of swimming — a similar kind of aid, more medium than tool — for channeling the inner life and improving the flow of thoughts.

The physical action matters just as much as the environment does. “The way we move our bodies further changes the nature of our thoughts, and vice versa,” the science journalist Ferris Jabr notes in an essay titled “Why Walking Helps Us Think.” It follows that the pace of swimming, because of its fluid continuity, encourages a specific kind of thinking. There are the same changes to our body chemistry in swimming as there are in land exercise: faster heartbeat, increased circulation, more blood and oxygen to muscles and brain.

Mr. Jabr invokes the peripatetics of Clarissa Dalloway, Virginia Woolf’s famously musing, ambulatory character, as someone who “does not merely perceive the city around her. Rather, she dips in and out of her past.” Woolf herself, writing in her diary about the stimulating energy of walking through London, used energetic, aquatic language to describe the immersive experience as “being on the highest crest of the biggest wave, right in the centre & swim of things.”

In his detailing of Stanford University research experiments on the relationship between walking and creativity, Mr. Jabr writes that walking set “the mind adrift on a frothing sea of thought.” For Mr. Jabr, Woolf and others, the choice of words betrays them. They talk of “ideas bubbling up,” the tumbling of them, the “wrinkling water” in a current of thought. Walking is conducive to thinking, but swimming is just as true a conduit.