Common Loons (Gavia immer) normally lay a single clutch of two eggs each breeding season. They occasionally lay one- or three-egg clutches, and rarely, four-egg clutches. Participants of the Canadian Lakes Loon Survey provided seven independent observations of loon pairs rearing four-chick broods. Photographic evidence confirmed two separate instances of adult loon pairs at Anglin Lake, Saskatchewan, and Kasshabog Lake, Ontario, exhibiting parental behavior toward a four-chick brood. Occurrence of four-chick broods may be the result of supernumerary clutches, nest parasitism, post-hatch brood amalgamation, or a combination of these factors.