It is nice at the Kemnader See because there is a separate cycle path where pedestrians walk towards you, but they have their own path, just like people who like inline skating. You can buy food and drink there or take a nice break on a bench.
The Kemnader reservoir is very recommendable. There are separate paths for walkers and cyclists. There are also restaurants and various water sports options. The Ruhr tent festival takes place at the lake in summer.