There is no better view of Pittsburgh's bridges and rivers.. than to be on it! This is probably one of my favorite activities while I was here visiting and definitely recommend it. Register to rent a single or tandem kayaks, get a life jacket, and be sure to buy a bottle of water! It's only $1 and if you're out there for a long time under the sun, trust me.. you'll want it. We were instructed that we could not paddle downstream at the time (not sure why, since we saw some other people head that way when we were heading in). If conditions permit, definitely make your way downstream for the really cool view of the fountain. One of the perks of having to go upstream first is that the trip back is a lot easier, especially if you're tired.
Watch out for other kayakers and the ducks that chill underneath the Warhol Bridge.