The swimmer with the wrong name

I'm standing at the edge of the pool in the dark, and the water is the colour of old coins. There's a woman doing laps, steady and silent, and I know I'm supposed to call her name when she finishes, but every time I open my mouth the name comes out different—Edith, then Margaret, then something I can't pronounce. She never stops swimming, and the water keeps getting darker, and I realise I've forgotten my own whistle.