If you only know Berlin for this:
You should come back and check out the rest.
Around one third of the city’s area is composed of forests, parks, gardens, rivers and lakes. Schlachtensee is one of them, south west of Berlin, between the Grunewald forest and Paul-Ernst Park, becoming part of Berlin since 1920 (map down below). It belongs geologically to the Teltow plateau, and was emerged some 15,000 years ago from the ice age as a glacial trough. It has a surface area of around 421,000m² and a maximum depth of 8 ½ metres, which makes it one of the larger lakes in Berlin. Situated on the east bank is the “fisher-hut”, a heritage protected historical guesthouse with beer garden and children’s playground.
The lake is popularly used for walking, jogging, cycling and for swimming, due to the good quality of the water and a seven kilometre long continuous boardwalk. In spring and summer time it will become crowded with people in swimwear ready to dive in with the “monster of Schlachtensee”. Fishermen also value the high water quality—and pull perch, white bream and gudgeons out of the waters of the tubular formed lake in order to catch a giant Wels Catfish, a common species here. It is not tasty, so it is then put again in the water, but it certainly does make a hell of a picture!
When the weather reaches 30ºC, which is not that often, we like to escape to the surroundings to feel relieved (although we actually live just beside one of Berlin’s big parks). A 1h calm ride by bike or a 20min trip in S-Bahn will do to get you to the heart of Paul-Ernst Park. I always prefer the bike. A ride across Grunewald is great for a refreshing shower of nature. Don’t forget food, a picnic cloth, refreshments and anti-mosquitoes stuff if don’t want to have to worry about stings next morning.