I've come up with two double drownings in Jamaica Pond. In this case, the victims are horses as well as men. Across the colonial and antebellum eras, history did repeat itself, first as tragedy, and then as Darwin Award entry.
New England Weekly Journal August 14, 1727
On Wedneſday last one Robert Sweedland, driving a Cart from this Place to Mr. Stone's Farm at Roxbury, drove down to Jamaica Pond, ſo called, in order to give Drink to the Horſes, and the Horſes being eager for the Water, ran ſwiftly into the ſaid Pond, and there were Drowned, and the poor Man willing to do his utmoſt to ſave the Horſes, was himself likewiſe Drowned.
Essex Gazette July 19, 1839
Sunday morning, a young man named Henry Whalley, was swimming a horse in Jamaica Pond, Roxbury, in presence of nearly twenty persons. The horse was kept in the water a long time, and urged far out from the shore. Becoming exhausted he rolled partly over, and threw off the young man, who not being able so swim, seized the horse so violently about the neck, that it was difficult for the beast to keep his head above water. Finally he gave a plunge and threw the man off, who sunk; after swimming around a few seconds, the horse also sank, and both man and beast were drowned. The bodies of both were recovered in about twenty minutes, but life was extinct. --- Boston Gazette.