昆明湖位于北京西郊颐和园内，北倚万寿山，面积3300余亩，约占颐和园的四分之三。昆明湖曾有七里泺、大泊湖等名称。

金时引金山（万寿山）下的水汇成金水河，称为金海。元代定都北京后，经水利学家郭守敬主持，开发上游水源，引玉泉山及昌平泉水注入湖中，改称瓮山泊（万寿山原称瓮山），成为大都城内接济漕运的水库。明代湖中多植荷花，周围种植稻谷，湖旁又有寺院、亭台，酷似江南风景，遂有“西湖”之称。清乾隆建清漪园时，将湖开拓，成为现在的规模，并取汉武帝在长安开凿昆明池操演水战的故事，命名昆明湖，每年夏天在湖上练武演操。

Kunming Lake (Chinese: 昆明湖, p Kūnmíng Hú) is the central lake on the grounds of the Summer Palace in Beijing, China. Together with the Longevity Hill, Kunming Lake forms the key landscape features of the Summer Palace gardens.

With an area of 2.2 square kilometres (0.8 sq mi), Kunming Lake covers approximately three quarters of the Summer Palace grounds. It is quite shallow, with an average depth of only 1.5 metres (5 ft).