Thank you guys for all the replies, it was very helpful.
To get out of the hole you're currently in, you'd need to either move to start afresh with new spirits of the water, switch to another food source while the spirits of the water calm down (if they do? The spirit of the water is still incredibly happy with me for the sacrifices in spring, when I fished last, and it's now autumn), or buy fish (salted/smoked/dried/roasted) in a village and sacrifice that. You can also sacrifice the last remainder of a roasted pike in the future.
Note that you can only sacrifice once per day per spirit (plus special ritual sacrifices), and the amount sacrificed doesn't matter, so a roach is as good as a salmon (or, put another way, sacrificing a whole salmon is a waste).
Oh, yeah, I have just gotten myself 32 dried breams through trade with villagers. Should I sacrifice all of them at once or only some part of them or just one? And should I do it everyday from now on? Also, where should the sacrifice take place? Should it be close to the water source or does it not matter, if the subject of sacrifice comes from a particular source (water, forest), in this case - water.
Also, does sacrificing a dried bream would have a bigger effect than sacrificing just a raw bream, since the first one is more valuable or spirits don't care about that, just as they don't with certain fish types?
In addition to angering the spirits of the water, you can also over fish, in particular in small lakes, so the catches dwindle, although they recover if given time.
That could also be the case, but I tried in many, many location with many attempts and it just stopped working. I was also fishing from a sea, because I decided to make my house close to the Njerpez cultural zone, but on the western side of that gulf in the south-eastern region of the map, so there should be a plenty of fishes.