Conclusion
The results show that as the river appraoched the sea, it became slower and less splashy.
In its earlier stages, Bob was often thrown into the air in wild and interesting poses. When he tried to climb out, we noticed that his hair was nice and clean. This confirms our hypothesis that material off the bottom was circulating in the water.
Farther downstream, Bob disappeared for much longer periods, and when we pulld him out, he was covered in slime and mud. So we concluded that the River ouse was in its deposition stage.
Bob was the most useful exchange student we ever had - so it's a pity really that we had to exchange him for another.