I'm looking for some comments on paddling the Cache River from Cache Lake to Kawnipi Lake. It appears to be about an 18 mile paddle on the river. There do not appear to be any good stopping points along the way, so I want to do it in one day (late July). If there are frequent marshy areas, it may become a very long day.

I have paddled the river 3 times. It is a shallow river all the way. There are some places to camp but they are not often used. The last 2 times I spent the night in a bushwhack camp and that worked out the best. Rather than try to finish the river in one day just plan on finding a place to spend the night. Most of the portages have enough space off to the side of the trail to spend the night. Try to take enough water from Cache Lake to get you all the way out into the big part of Kawnipi.

Thanks for the input, MagicPaddler!

Have done this twice in past years and this would be a very long trip to do in one day. I agree the only places to camp are at the portages, and do not expect much.
A campable dry area near the mud is what too expect.
The only escape from this stretch is a portage about half way south into Ferguson Lake, one of the nastiest mug bog portages in the park, and so bad it was removed from the map in the 1990's.
The entire river is an interesting winding small stream surrounded by mud marsh on both sides that let you know to stay on the stream.
When you finally get close to Kawnipi, there are 3-4 portages where you step from rock to rock around small rapids, and finally a portage around a waterfall into a narrow northern narrow part of Kawnipi.
To summarize: A Great Adventure! Do It!

I forgot to add: Take water. You do not want to do the Cache River without adequate good water.

The portage that Eyedoc talks about is the way I have gone most of the time but there is a nice portage on the south side of the river that goes around all of that. The nice portage has not nice landings on both ends. The Adventure map has the portages marked but the scale is such that you can’t tell which side of the river they are on. PP has the portages on a good scale.
EDIT
After you get on Kawnipi you have about 3 miles to paddle to get good water.