I can tell all of you that was without a doubt a fish,there can only be one answer for what kind of fish. I also grew up fishing the Missouri river and the only logical answer to me would be the largest freshwater fish in north america...The White Sturgeon..known to grow up to 1,799 lb and up to 20 ft. it was no buoy that was without a doubt a fish...and that was no average fish,whatever it was i'm sure was in the area of 1,000 lbs or better.the Missouri is a huge ancient river that also flows to the pacific ocean..could also have been a Bull Shark they have been caught as far up river as St.Louis Missouri...
Look at the side of the river and make a reference point for where they are. At both the start of the video and the end of the video, you can see on the right bank that they hardly move at all, and instead it's the current pushing the boat backwards that makes the object 'move past' the boat, and without realising that they've been pushed back, they stick on the motor and go past it again to only be pushed back again when they turn the motor off to let it 'catch up'. To answer the bobbing and weaving thing, currents can make loose underwater objects do that. I don't think anyone could place a bet on exactly what it is, but I'm guessing it's some object that got snagged on something like a rock or some weird plant as it flowed downriver.
Really nice, low budget special effects. Log or something stuck underwater in the fast-moving current. Pull your boat up to it, shut the engine off, allow the boat to drift backward with the current making it appear that "the fish" is moving away. Start the engine pull back up to the sunken log, repeat.
