Veterinarians are warning New England residents that a quick swim in a pond can turn into a life-or-death emergency for dogs. Pet owners should be aware that blue-green algae, or cyanobacteria, can appear in warm, stagnant water and make pets severely ill within hours. Here's what to know Boston's Angell Animal Medical Center advised pet owners to be careful around ponds, lakes, and other still water, as The Daily News of Newburyport reported. …