Not in the sense for carnivorous plants. Most likely the river water will contain dissolved minerals not to mention organic matter and other stuff from being dumped in the rivers. The oceans are “salty” because of the dissolved minerals that are dumped in from rivers and streams over eons. This probably would not be in the best interest of your plants. However the only way to be sure, and you really want to pursue this is; to take a sample and have it tested, maybe contact your Extension office to ask if they could test it for you, you will probably be charged a nominal fee.
Now I use rain water almost exclusively and quite successfully for my plants, however I take precautions before I collect it; mainly, I make sure I collect it when there is a somewhat “heavy” rain and my roof has been flushed off good, and the hoses are flushed out before it goes in my barrel. I do this with the use of a valve system. I have seen this first hand, how much difference this makes on the cleanliness of the water collected. I have also used melted snow.
For more info on my system it can be found here:
http://www.flytrapcare.com/phpBB3/viewt ... 696#p12696 hope this helps a bit.
Good growing and good luck
Bud