Shanhaiguan Yansai Lake Yansai Lake, also known as Shihe Reservoir, is located in the tourist city Shanhaiguan, located at the foot of Yanshan Mountain, with beautiful and elegant ecological environment, is an important part of Changshoushan National Forest Park and Qinhuangdao Liujiang National Geopark. Yansai Lake Scenic Area has been a skyscraper of the military fortress Shanhaiguan since ancient times, and ethnic military conflicts in the Sui, Tang, Liao and Jin periods have occurred here.