Introduction to lakes and mountains: Daihai was called Tianchi in the "Book of Mountains and Seas". It was called Yanze in the Han Dynasty, Shenhepo in the Northern Wei Dynasty, Xiaoshui in the Yuan Dynasty, and Daihabo in the early Qing Dynasty. Called Daihai, it is a structural freshwater lake with a total area of 154 square kilometers and is formed by the intersection of 22 surrounding rivers. The lake is shaped like a long east melon. It is about 25 kilometers long from east to west and 10 kilometers wide from north to south. The average water depth is 7 meters, the deepest can reach 18 meters, and the water storage capacity is 1.3 billion cubic meters. The average temperature in July and August is above 20 degrees Celsius. From 9 a.m. to 5 p.m., the water temperature is above 20 degrees Celsius. The monthly maximum water temperature is about 27 degrees Celsius, which is similar to the sea water temperature in Qinhuangdao and basically meets the international natural bathing beach standard of water temperature above 23 degrees Celsius. The bathing beach in suitable waters on the northwest coast of Daihai Lake has a capacity of 3,000-4,000 people and the water quality is good. There are now 27 species of fish living in Daihai, especially carp and fish are famous far and wide. The large whitebait is exported to Japan, South Korea and other Southeast Asia.