The water from this little lake flows into the Zartenbach stream. It is located between Hinterzarten and Feldsee, in the Eschengrund nature preservation area. Luckily, it can only be reached by foot. To get there, follow the Emil-Thoma path from Hinterzarten, heading southwest i.e. towards Feldsee, Feldberg, and Rinken. Then turn left after around 2 km (signposted). After about 500 m, you will have reached the moorland lake.
In the winter, the Oberzarten cross-country ski trail leads past Lake Mathisle.