I drove past new apartments on Lady's Bridge called City Wharf. "Strange" I thought.. "a Wharf on the Don". Then I noticed that it's really wide as I drove over the bridge by the Hotel Bristol multi storey.

Does anyone know how far could you get a sizable boat up the River Don?

Don't quote me on this but i persume you can get to the sea.
The Don starts at Goole which comes out of the Humber which starts from the North sea.
On the other end of the river the Don runs toward Stocksbridge.
After tha i loose it but persuming it can only go two ways from there one being Manchester therefor running into the Derwent or Huddersfield.
As i said don't quote me on this.

afaik the source of the Don is out by the Flouch crossroads, when i worked in the microbiology department at sheffield uni we used to go out there to get samples of the Don as a control before it stated getting polluted in Stocksbridge

as to how far you can get a barge or similar up the Don it wont be that far because of all the wiers, so basically the question is where is the first wier, coming from the sea, on the don?

This link should help.

http://en.wikipedia.org/wiki/River_Don%2C_England

The river going out towards the Flouch through Stocksbridge is the Little Don or Porter (not to be confused with the Hunters Bar / Ecclesall Road Porter).

The source of the Don is up on the moors to the west of Dunford Bridge (west of Penistone & south of Holmfirth).

I can't ever recall seeing anything sizeable on the Don in Sheffield as it is pretty shallow - in fact the only time I can remember any "boats" of any description on the Don was once a year when the students used to have a "boat race" of sorts as part of rag week. The "craft" mainly seemed to consist of rafts and bathtubs. The students where quite foolhardy given the level of pollution in the Don at the time (late 60's).

Perhaps worth reviving this tradition now the Don is much cleaner?

This ones even more informative.

http://www.waterscape.com/waterwaysguide/waterways/South_Yorkshire_Navigations/South_Yorkshire_Navigations.html