Yes, this was quite a common trade way in this times: Raseiniai via Dubysa- Seredžius via Neman Tilsit (Russian: Sovetsk)-Weynothen (Russian: Istok) via Gilge, Russian: Matrossovka  until 4,5 km before Gilge (Russian: Matrossovo) via Großer Friedrichsgraben (Russian: Polesski kanal- Labiau (Russian: Polessk) via Deime (Russian: Dejma) - Tapiau (Russian: Gvardejsk) via Pregel (russian: Pregolja) - Königsberg (Russian: Kaliningrad)
Sounds difficult, but was easy shipping, also used for wooden rafts. I think, the trip took three days. The waterways of this route were for the most part on Prussian territory. They were kept in good order by the Prussian state.
On the river Gilge rafts were allowed, which were up to 100 m long and up to 10 m wide.

Ruth Leiserowitz