I do not want to get anyone killed, so take this with a grain of salt and use common sense. but if I was going to ice-fish a river I would follow these steps to cheak the ice thickness
1 get someone to come with you for safty reasons
2 get 50 to 80 feet of Good 1/4 or thicker rope.
3 tie off to a large tree or other object and to your waist
4 every five feet on teh ice cheak the ice with a Spud (ice chistle) untill you think you are out far enough, then cheak an other 30 feet.
If you do fall throw you will be able to pull yourself back out of the water with the rope ( or at least teh cops will be able to find your body easyer