The routing engine will choose routes that cross fords. I think this is the right routing decision - in many cases the fords are readily crossed. Here is one that is not safe to cross after a rainy day.
Perhaps fords could be more prominent on the map view or mentioned in turn by turn directions. Then the rider could make a judgment call ahead of time based on weather and the size of the river.
Workaround: Some of the OSM map layers indicate fords at high zoom levels, but this is pretty cumbersome to inspect for a full route.
Or maybe this is unique to New Zealand 😀 and an edge case. I have encountered both bridges and fords on both paved and unpaved roads.