You know, the river's shallowness is actually somewhat of an asset. Because it's too shallow (at least through downtown) to allow easy boat traffic, planners could easily implement a riverwalk that is wide enough to allow seating, temporary shops/restaurants, and entertainment. On a deeper river, the encroachment of a boardwalk like that would be unacceptable because it would impinge on river traffic, but in GR, that's not a problem. Incorporate some wetland plantings as part of the boardwalk (for example, have an "empty" space between the boardwalk and the retaining wall that is filled with native plantings), and you could have an attraction that few cities could match.
It also seems like that kind of a setup would have to be concentrated on the west side of the river for now. It's been a while since I've been downtown, but I seem to recall that the east side has a decent, if not perfect, walkway already. A riverwalk that traverses at least the immediate downtown area would be a huge improvement over what's there now!