A lot of Idaho's rivers are popular for sports.  During the summer probably the most heavily populated section of river is the six mile run from Barber Park to Ann Morrison Park on the Boise River. The season usually begins in late June.  The exact date can depend on the previous winter's snowpack, which in turn affects the flow rates released from Idaho's dam system. In early June flow rates are often dangerously high. The season begins when the flow rate is reduced to a "safe" level. During the rafting season there are shuttle busses running between Barber and Ann Morrison Parks. Information is available at:
http://www.adaweb.net/departments/par...
 
There are fees for parking at Barber Park.  Parking at Ann Morrison Park is free. You can load inflable equipment on the bus for no extra charge.  If you want to use hardshell canoe or kayak, you need to arrange your own shuttle.  Hardshell boaters often like to put in at the end of E. Parkcenter Blvd. This location is downstream from the first (and steepest) diversion dam. Canoeists often prefer not to go over that one.  So far there has been free parking by the Parkcenter put-in, but that may not continue as development moves in.  A trick about Ann Morrison is that you can enter from the north (Americana Blvd) end and drive all the way through.  If you enter from the south (Royal Blvd) you run into one-way-do-not-enter lanes a short distance past the center of the park where you wait for the bus.  If you have difficulty finding a parking spot from the south side, you could take W. Crescent Rim Drive around the park to the Americana Blvd entrance.  This will give you access to more parking spaces.
The take-out at Ann Morrison Park is by the footbridge. If you miss it you still have room to get out, but don't go too far.  You do not want to go over Americana Blvd Dam.

Rental equipment is available from Ada County at Barber Park, although it's pricey.  You can drop it off by the truck at the bus stop in Ann Morrison Park.

Although you will see many people without PFD's, you should wear them.  There is a danger of getting caught in branches along the river.  There is also poison ivy along the river from Barber Park to Municipal Park.  It is often camouflaged by the cottonwoods.

A visor or hat to shade your eyes from the sun is recommended.  The river has claimed many eyeglasses and sunglasses.  A retainer can prevent that.

The shuttle busses usually stop running after Labor Day.  Enthusiasts often arrange their own shuttles, usually into mid-October. After that the flow rate is too low.  In October the poison ivy turns red and is easy to distinguish from the cottonwood, whose leaves turn yellow. Virginia creeper's leaves also turn red. Berries of poison ivy turn yellowish-white.  Berries of Virginia creeper turn blue. 

Alcoholic beverages and glass bottles are prohibited on the Boise River.