Rhea!

For 17�, you can board a boat called "RHEA" and cruise around for 2 hours in Jyv�skyl�'s lakes.
Make sure you bring cash for when you board (I went with a knitting group and we had reserved a table), and they have a menu in English and Finnish.  They accept Visa Electron, cash and I assume all major credit cards.
It was from 7-9pm and can get a little cool on the water, as the sun dips lower.  But it was lovely seeing all the nice greenery, lots of open space and some really nice houses!
There's a nice, soothing voice in both Finnish and English explaining a bit of the areas you're in - but it's not constant talk like on a tour bus.  You can sit inside at some tables or outside.  (We opted for outside and ended up eating outside too).
They do serve alcohol and other non-alcoholic beverages.
So make sure you bring your camera!  Here's some photos I took:

A young man baiting his hook...

A duck that was quite slow at swimming away, as we cruised along!

A chicken salad...

The white chocolate cheese cake!  It was really great!

My friend's blueberry cheese cake!

The sign said something about "The Maximum Loading Weight is 50 tonnes".   I still don't know if that applies to the boat, the water or the dock...but we posed around this sign and had a good laugh.

Oh and FYI - the horn's really loud if you're sitting outside and near the front of the boat.