The Irsee Lake, which is 5 km long and up to 1 km wide, reaches up to 27 degrees Celsius in summer. There are numerous beach pools.
The Irrsee is located in a nature reserve surrounded by a moor landscape and is due to its small volume and its sheltered location the warmest lake in the Salzkammergut.
Together with Lake Fuschl, it is the uppermost lake in a chain of lakes that continues over Lake Mondsee to Lake Attersee. The Irrsee is considered to be relatively natural and therefore offers a habitat for many endangered animal and plant species.