Trout, the ship that sails against the current

The small boat is quickly put together. 

You don't need glue because the wooden boat parts will swell a little when immersed in the water and therefore hold together tightly. The trout’s paddle wheels are driven by the water current. 

First, the boat floats away with the current, unwinding the line. 

As soon as the line is unwound, it continues paddling happily, only it returns against the current.   Assembly from age 9, play from age 6.