For a voyage down the city’s main river you go to the quay in front of the Landesmuseum (Swiss National Museum). There are cruises from April to October, with boats departing every half an hour.
And in the months of July and August you can make the trip any time between 09:05 and 21:05. It’s a journey well worth doing as you’ll be granted a beautiful perspective of Zürich’s Old Town, which sprawls across both banks of the river.