A river is (typically) going to be much shallower near any islands, though... just as it's shallower near the shoreline on either side, it's shallower near the shoreline of the island.
The *height* of the river water doesn't change, but the height of the *land* beneath it does.
The land doesn't just drop off and disappear, giving you a floating pile of earth. TECTONICS don't form river islands. It's not the ocean. EROSION and LAND HEIGHT forms river islands.
So *every* island, especially the ones that are closer together, are going to help with crossing that river ... and I'm sure that includes bridging it.