New Jersey’s largest lake was the setting for a festive polar plunge on Saturday. Hundreds were expected at the 14th annual Leap in the Lake, held at Lake Hopatcong and organized by Lake Hopatcong Elks No. 782. Plungers dashed from the beach at Hopatcong State Park in Roxbury into the frigid waters starting at 1 p.m. All donated a minimum of $50 to participate and proceeds will benefit a program for children with special needs, other youth services and building renovations, according to the Elks chapter. Rick Gathen of Stanhope, founder of Leap in the Lake, said the event has steadily grown fr…