While aboard a yacht, the tennis pro cradled her growing belly donning a black one-piece bathing suit.
Earlier this month, she shared a mirror selfie showcasing her chic and casual maternity style.
Also in May, Williams and fiancé Alexis Ohanian radiated the red carpet at the 2017 Met Gala held at the Metropolitan Museum of Art in New York City.
The mom-to-be was glowing in a green Versace gown and shoes, paired with an Audemars Piguet watch, and XIV Karats earrings.
The week before, Williams shared a baby bump selfie and a heartfelt message for her baby on-the-way.
In April, Williams announced her pregnancy news. She is expecting her first child with her Reddit co-founder fiancé, 33.
The couple were engaged in December.