Someone told me the native Athabascan name for the Knik River meant "The Silt Monster", and a silt monster it is indeed. Though fairly shallow throughout, it is in places over a mile wide and pours a massive amount of grey, silt laden glacier water about twenty miles from the Knik Glacier to the Knik Arm of the Cook Inlet.
If you start at the source (the Knik Glacier) the river is at first a swift class two... very cold and fun but without many of the dangers of other rivers (strainers and large rocks are very few in this area, basically there are dunes of sand and silt on both sides that don't present major obstacles. As you continue to float down it descends into the classic Alaskan "braided stream" configuration, basically small, shallow, swift moving channels amongst islands of silt.
After about three miles of this the braided stream breaks up and the river opens up into a broad, straight river with slower current and fewer "silt island" obstacles. This part is an easy class I that you could do as a family float or in an open canoe. As you float this stretch there will be beautiful scenery as Pioneer Peak rises on your left with snow capped peaks and hanging glaciers as well as dense Alaskan forest.
I've seen black bear, moose, beavers, porcupines, and many bald eagles in this area. Along this stretch the river breaks off into a series of channels, with forested islands in between them... with many nice spots to stop for a picnic. As you continue to float, eventually you will hear the sounds of the Glen Highway, and it is time to start heading for the boat take out point on the north side of the river underneath the Glen Highway Bridge.
Overall the Knik River is one of the most easily accessible floats in the Anchorage area but still provides an authentic Alaska experience.
The Knik River is about nine miles away from Wasilla and Palmer, large (by alaska standards) suburbs of Anchorage which offer all the services you would need.
From Anchorage proceed north along the Glenn Highway about 35 miles until reaching the "Old Glenn Highway" exit. Take the exit and head east approximately ten miles until coming to the "Old Glenn Highway Bridge". You can park on either side of the bridge.
The easiest put in is at the Old Glen Highway bridge, as there are large sandy banks where you can park your vehicle and walk to the river to put in. If you are a packrafter you can park your vehicle here and hike approximately 10 miles northeast along what is known as the "Jim's Creek Trail" to put in at the actual Knik Glacier (the view is worth the hike) and enjoy the fast braided streams of the upper Knik before it opens up into the broader, slower class I downstream. The normal take out is underneath the "New Glenn Highway Bridge"......where there is a primitive concrete boat launch just underneath the bridge itself.
Just a warning... the Jims Creek Trail system is most popular with the 4-wheeler crowd, which can sometimes get a bit rowdy (lots of alcohol and the occasional shooting of guns in the air)...just beware of this if you are hiking the trail to packraft and stay off the most popular trails and close to the river so you don't get run over.
The boat store "Alaska Raft and Kayak" in Anchorage has all the info you would need to float pretty much any river in the Anchorage or Kenai areas.
"The Alaska River Guide" by Karen Jettner