Yeah, that's the point.What's the point in crossing river whem you search in forest?
Even if you succeeded in skill check you will get a parasite or lizardbeast encounter (and of course you clotches will be all wet)
Either walk naïvely into the river and catch a parasite.
Or walk knowingly into the river trying to catch a specific parasite.
If you don't like lizards, wet clothes or parasite, you better ignore rivers.