COLUMBIA, Mo. (AP) — On the first Tuesday in July, Linda LaFontaine's paddle cut through the hot, heavy air and sliced back into the murky water of Perche Creek. Keeping pace with her teammates, her strokes were quick and methodical, powering the bright blue paddleboard toward the Missouri River.

On board was Cami Ronchetto, LaFontaine's former co-worker and cherished friend. Paddleboarding is a new challenge for the pair, but their team chemistry is rock solid. They have raced together competitively in kayaks and canoes over the last decade.

The first competition they tackled was the Missouri...