ANOKA, Minn.—A veteran triathlete had to get rabies shots after she was attacked and bitten 25 times by an otter in a northern Minnesota lake. Leah Prudhomme, 33, of Anoka, was doing a regular 1.5-mile training swim in Island Lake, 17 miles north of Duluth, on Wednesday evening. As she passed by a bog on the last stretch, she felt something bite her ankle to the bone: an otter. She screamed for help as her father and young children watched from the shore. Prudhomme sustained 25 bites—some more than 2 inches deep—before her father could rescue her in a boat...