I haven’t had exactly the same problem, but definitely something close. I can place fishtraps in fairly shallow water on the edges of deeper water (for example close to banks on noob river or at priestking’s retreat), but I can’t place fishtraps anywhere in the boundary spillway (and get the same must be placed in water error. I haven’t tried either of the western or eastern rivers - I’'ll try to get round to testing them when I have some time.
(I’ve reported what I encountered - probably be good if you report it to helpshift too, since you have different evidence - Contact Us — Conan Exiles Help Center )
I’ve now done some testing and can confirm i’m finding the same thing as you with the Eastern and Western Rivers (and the central branch that joins them). Once you get far enough down the Eastern River to be past the last waterfall - just before Bonebreaker’s Bend - it becomes possible to place again. Even more confusing is up towards Priestkings Retreat, where the division point between can place and can’t place looks exactly the same and is just within the same stretch of water.
I’ve reported these findings to helpshift as well (with screenshots and map).
these parts of the river that are super shallow might not actually have water physics volumes, which would cause that bug (i had the same thing happening in my map mod cuz i be dumb). i’d have to look in devkit to be sure, but if that’s the case it should be an easy fix for them in the future. keep reporting stuff like this , inflexion seems to be really good about feedback and actually following thru on stuff!
I can confirm that it’s probably missing the water physics volume. You don’t get splashing sound effects, you don’t get the water interaction physics, nothing. It’s the same for almost ALL shallow water in the game right now: From the western and eastern rivers, to the shallow water in the jungle. They DO have the ‘water’ tag to make it drinkable, but it’s missing the physics volumes altogether. I’m guessing the folks who did the Enhanced version didn’t think shallow water needed the physics volumes since it’s shallow water: Not realizing that would make fishtraps stop working lol. But yeah, it should be a really easy fix. The Devkit just finished, I’ll go take a look myself if you haven’t yet actually!
Added strangeness then - Boundary Spillway has the same problem of ‘Must be placed in water’ for fishtraps, but does have the splashing sound effect when running in it (since today’s update).
Since yesterday’s patch, this seems to have been fixed (at least in my game). Fishtraps can now be placed normally.