Sara Bishop and her roommate have relied on the Deering Oaks pond for the past three years to help combat the winter doldrums. They make the short walk from their St. John Street apartment to the 3.5-acre pond in the evening, when artistic lights turn the park into a majestic winter wonderland. “It’s so beautiful and no one else is normally on the ice at night,” said the 22-year-old Bishop, who used to travel from Gorham to skate on the pond. But this winter, skaters like Bishop will have to travel to rinks in outlying neighborhoods, including a new one at nearby Thompson’s Point.