[i](There doesn't look to be a safe way to get there... Two hundred feet of churning water on each side of the island.
A few problems with your spell. First, it isn't simply a surface that cannot support your weight -- it is a surface that will hit you sideways at time. Second, maintaining concentration is not a given -- and if you fall into the water, there is a very real risk of drowning.
Third, there are other people travelling the road, and boat anchored not too far downstream, where merchants load and offload their cargo moving along the river. Although it is not automatic, someone could see you.
Note that you only add Artes Liberales if you spend 15 minutes (per magnitude) preparing the spell, with candles, drawn pentagram, and/or other stuff like that. Again, not very practical in a place where mundanes can just arrive at any time.)[/i]
After casting his spell, but just before he steps on the churning water of the river, Torros gets hit by a sense of danger. He feels like he cannot breathe, as he is drowning. The shock of his sudden premonition break his concentration, and his spell ends.