Give Cascade Lake & Creek a try. Plenty of carp, bass and panfish to keep a guy busy for hours.
Just keep your eyes open for Wild Parsnip that lines the banks of the creek.
Another option, while not in the city of Rochester, would be to drive 40 minutes over the Mississippi River and fish some of those areas. Places around the dams and spillways, many backwaters, and places like Prairie Island in Winona are all very popular shore fishing areas.
Also, Rochester is a real trout-friendly area. That's as shore fishing friendly as it gets. Head down to Trout Run or Whitewater state park for an afternoon of fun fishing, preferably when the water temps are a bit lower (and the fish are a little more eager). Bring a mepps spinner or a floating rap, and go to town. It's also a good opportunity to pick up fly fishing, if you ever get the desire. Those trout creeks are a GREAT way to cool down on a warm afternoon, and this time of year you won't need expensive waders. Just a pair of pants and some old sneakers and start hiking. I spent thousands of hours on the creeks of SW WI and SE MN (more on the SE MN side) and can tell you that some of my most memorable days of fishing ever, came on some of those small streams.
Here's a link to the trout maps that the DNR has online. http://www.dnr.state.mn.us/fishing/trout_streams/south_mn_maps.html
Remember to pay attention to where the angling easements are, or ask permission if your not sure. In Minnesota I can tell you that I was never once turned away by a landowner if I first asked permission to fish their property. Landowners always seemed genuinely shocked and pleased that someone respected their property enough to take a few minutes to say hello and ask permission. Sometimes you'll even get a few tips as to where some of the better 'holes' are on the creek, or where their bulls are so you know where NOT to go.