Lake Sagami (相模湖) is an artificial lake located northern Kanagawa. It is popular recreation spot for Tokyo people because it is very easy access from Tokyo. There are many activities for visitors such as boat riding, fishing, cruising and hiking. In summer there is a fireworks, and also there is camping spots around the lake.
Tourist Info.
There are parking, restroom, restaurants, gift shop and other entertainment facilities.
Access
0. at Shinjuku Station
1. use JR Chuo Line to Sagamiko (56 min.)
2. walk south
3 hr.
New Wave Samurai Movie. 
映画好き集まれ！ 
After Tokyo Olympic, Lake Sagami became very famous canoe and boat spot.
Lake Sagami offers great Sakura in Spring, beautiful green leaves and fireworks in Summer, awesome Autumn leaves in Falls, and Wakasagi fishing in Winter.
There are restaurants, and hotels.