In July 2020, the main route for commercial ships in Kattegat, Route T, was split into two: one route for large ships and one for smaller ships closer to the Swedish coast. The potential effect of this major re-routing on the marine environment, for example on the communication space, is investigated in this study. In particular, the focus is the harbour porpoises (Phocoena phocoena) and one of their prey, the Atlantic cod (Gadus morhua). Both species use natural sound for orientation and cods communicate at low frequencies (<200 Hz). Data on ship movement, wind, sound speed profile and both modelled and measured sound levels were recorded for one year before the rerouting and one year after. In addition, two methods were utilized to study any impact of the change in environment on the selected species. The results revealed a generally high sound pressure level along the shipping lanes. The rerouting increased the noise, in the 1/3 octave band with the centre frequency of 100 Hz, along the coastal route, in both northern (by 5-6 dB) and southern (3-4 dB) Kattegat. The shipping noise has also extended over a larger area. The acoustic habitat quality in terms of communication range has decreased for species like the cod but not for harbour porpoises. However, their ability to detect natural sounds has been reduced. The harbour porpoises potentially avoid larger areas due to more ships in the new shipping lane after the re-routing.