Another important quote from chapter ten is "... She would not join the groups in the sports and bouts but... she swam out alone." The sea symbolizes independence and freedom. Edna would not join the groups, which symbolize society's conventions. Instead, she ventures out alone into the sea where she's free to do anything as her will pleases. She's determined to be independent and unique, unlike the rest.
"A quick vision of death smote her soul, and for a second of time appalled and enfeebled her senses... she managed to regain the land... She made no mention of her encounter with death..." The sea foreshadows Edna's eventual death at the end of the novel.
The sea is used repetitively in the novel to emphasize its importance to the reader. The sounds of the sea constantly seduce Edna throughout the novel.