Aerial photo taken on April 10, 2019 shows tourist boats sailing near a pier on the Baiyangdian lake in Xiongan New Area, north China's Hebei Province. Restoration work has started in Baiyangdian Lake, northern China's largest freshwater body. High-pollution and energy-intensive production has been tackled. As a result, water quality has improved remarkably. (Xinhua/Mu Yu)