The source of the river is the Aachtopf in Aach, the largest spring in Germany, at a height of 475 m above sea level.

The last six kilometers of the lower course flow through a nature reserve called Radolfzeller Aach Ried.

There are also noticeable stocks of some other endangered fish species, such as lamprey and European bullhead, who enjoy their protection close to the bottom of the river.

Canoeing in the section between Aachbad Singen and Bohlingen, however, is not advisable on account of the many water discharges and heavy industrialization.

The lower reaches of the Aach are a nature preserve and closed to water sports year round.