The Gudenaa Å river starts from the village of Hesselager and flows through the eastern Kolindsund until it reaches the mouth of Grenaa Harbor at the Kattegat Sea. It spans approximately 7 kilometers in length.
Initially, the outlet of Grenaa River served as a crucial passage for ships entering the strait, as it was once part of the now drained Kolindsund Lake. However, the significance of the river declined with the drainage of Kolindsund.