When the city hits thirty degrees, the plan is simple: get out of the centre, get in the water, and find some shade with a cold drink in it. This is a pick-list, not a route, so grab the stop nearest your patch and build the afternoon around it.
For the swim, the Houthaven gives you a sheltered dip in the west and the Nieuwe Meer is the big open water in the southwest, with room to anchor and slip off the boat. The richest run is out east, around the Oostelijk Havengebied (the eastern docklands): the Diemerpark has a green, monitored swim spot on the Diem, and the old harbour islands are dotted with purpose-built jetties, the Levantkade and the Borneokade zwemsteigers (swim jetties) and the Bogortuin steps on Java-eiland, where you tie up and drop straight in. Out past them, IJburg's Blijburg is the closest thing the city has to a beach day on the water.
For the shade and a cold one with the boat in sight, Café de Ceuvel up in Noord does both at once: tie up, swim off the deck, then dry off with a drink right there on the water. Out east there is a terrace for every mood: Eetcafé KANIS on the Levantkade sits a few steps from that swim jetty, Sham Oost has its own steiger (jetty) and a waterside terrace on Borneo, Brouwerij 't IJ's Café Struis pours its own beer near the Zeeburgerstraat, the tiny Café 't Sluisje holds the old lock on the Nieuwendammerdijk, and Brasserie Vrijburcht has the calm community terrace out on IJburg. Back west, Het Bosch sits on the waterfront by the Amsterdamse Bos and BRONS is the easy terrace call on the Postjesweg.
A few honest notes. Swim only where it is meant for swimming. Some of these are official zwemlocaties (the city's marked, monitored swim spots): the Nieuwe Meer, the Diemerpark, and IJburg's Blijburg among them. We carry their live zwemwater.nl status right on the spot page, refreshed daily, and it does move, so a green GOED (good) one week can read a red WAARSCHUWING (warning) the next: check it there before you get in. The rest, like the Houthaven and the jetties out in the eastern docklands, are open water and swim-at-your-own-risk, so mind the boat traffic and the cold. Shade on an open boat is on you, so rig a cover and bring more water and sunscreen than you think. The good terraces fill the moment the sun lands, so an early lunch beats a late one. And the docks and free quays go first come, first served, with the signs on the quay the final word, so read them before you tie up.