Some swim coaches are classified as "yellers" or "shouters" because they call out instructions to their swimmers while they are in the water. As a young swimmer, I had a yeller coach, and I never heard what she said. I could see an animated adult trying to shout instructions from her poolside location or, sometimes, running next to me with her mouth moving and face flushed. I knew sounds were coming out, and they seemed important, but I couldn't hear what they were.
When I became a coach, I succumbed to the same temptation for many years until it dawned on me that my swimmers had no idea what I was trying to say as I coached them in practice or at meets. So I decided to coach silently.
I created coaching cards with various short and easily read "Swim Thoughts" on them that communicated visually to my athletes what I wanted them to do to go faster or perfect their technique. I laminated these cards and carry them with me to practices and meets. They are like cue cards. (Sometimes I still go up and down the pool, to coach a more pronounced kick, or to get a tighter breaststroke streamline, but I try and demonstrate it visually.) I have refined this technique in practice by presenting and explaining the card with the appropriate Swim Thought on it to the group at the beginning of a set to reinforce what part of the stroke I want them to work on. I will also display it during the swim or set as a reminder. Then after the swim or set, I ask if they could see the card, especially if I don't witness them kicking more or streamlining well.