We've walked on that River Walk. Glad we weren't doing so when the piece broke off, although it appears that, thanks to the Mavis, we'd have had a fairly uneventful ride down the river.
We've watched little river tugs like this at work on the Fraser River and across the Strait in Ganges on Vancouver Island. Pretty amazing what these guys can do with a simple little boat. No bow or stern thrusters, either