The Mercer Island Polar Bear Club will welcome in the new year on Saturday at noon at Clarke Beach, when a group of 20 to 50 people will brave the chilly waters of Lake Washington. Organizer Nile Clarke said this is the oldest Polar Bear Club in the area, with the first plunge in 1968. Clarke Beach is named after his grandmother, Mabel Clarke, who came to Mercer Island in 1906 from Iowa with her husband, Fred. Mabel Clarke was an avid outdoors person and an Island pioneer, so the city named the park in her honor.