Any fisherman at the waterfront will arrange a boat trip, and negotiating directly is both cheaper and more interesting than going through an intermediary. Trips range from a short hour-long cruise to a half-day journey upriver to where the plantations give way to denser bush. The boats are simple wooden craft, low in the water, and you sit close enough to the river surface to feel genuinely close to it.
The coconut plantations that line the banks supply a significant share of Tanzania's coconut production, and if you ask your boatman he can stop at a processing point to show you how the nuts are husked and dried. Hippos are most visible in the morning and late afternoon when they move into shallower water. Keep your hands inside the boat. Sunset cruises lasting about 90 minutes are the most popular option and run every day conditions permit.