Good on warm summer days. Wetsuit needed on colder summer days. Otherwise a wetsuit is always needed, during winter a thick wetsuit. Since the lake is about 500m above sea level, it is always a bit colder here.
Drive on A3 and take the exit to Limburg-Nord and onto B54 follow signs towards Siegen and Rennerod. Then take B255 towards Herbronn and follow signs to Mademuehlen and the Krombach Talsperre. Here you will find the camping ground Mademuehlen-Driedorf.
The spot is located at a camping ground. You need to pay fees to access it, but therefore you can use the facilities. Stay in the designated windsurfing zone, specially during summer. Stay away from the north shore, since it is a natural reserve.