I agree with Bob. In my experience Hummingbird did not stack up. If you are interested in a fish finder that works well in the relatively shallow depths of rivers you need to look into the following features:
1. Resolution. Pixels are the key. More pixels per inch will provide better detail of structure, and will pick up suspended fish like sturgeon.
2. Transducer angle. Some manufactures let you decide between different tranducer angles. For example an 8 degree angle will not have the coverage that a 20 degree angle has in river depths.
3. Side scan. A great feature in rivers when fishing for salmon or steelhead. Allows you to "see" off to the sides of your boat rather than just strait down.
I have researched all of the major manufactures. Features like Total power, pixel count, display size, frequency, speed, distance, and temperature, alarms, ect. I have owned several including Eagle, Lowrance, Hummingbird, Raytheon, and Garmin. All were top end models. In my opinion, there are two that stand out. The Lowrance X-85 and one that I currently use is the Raytheon L750. This has been by far the most reliable and useful fishfinder I have owned. It works fantastic for salmon, but it really shines for sturgeon. It picks up suspended fish as well as fish on the bottom. A great unit! Good luck!