Subeden, Day 5: Dead waters

Day 5
Note on the physiological effects of life in the Subeden:
Despite being rich in discoveries my stay in the area had been quite uneventful so far. This environment felt surprisingly peaceful, one might say welcoming, and I had not yet identified any major danger.
Nevertheless, I found today that I was right in taking the necessary precautions. My suspicions were triggered when surveying the coastal areas where I couldn’t help but observe the apparent lack of macro-organisms in the Amarina waters.
Intrigued by this observation I ran some basic analysis of water samples from both the small surrounding affluents and the sea itself. While the small creeks showed nothing unusual the glowing golden essence of the Amarina showed the presence of a few highly toxic substances, close in nature to some dangerous surface-dwelling mushrooms.
The source of this contamination couldn’t be identified by the available tests yet it makes sense that it is produced by the encircling mastodons. Very much worried, I collected samples throughout the closest creeks. Thankfully the contamination does not extend upstream.
I have now stopped exploring the coast without a full body suit and the highest caution. The running waters in the valley overhead will keep providing me with drinking water but regular tests will be done. In fact, I have some irrigation infrastructure planned in case I decide to stay here any longer.
Could poisoning have been the reason for the loss of previous explorers in this cave? Skepticism engulfs this theory as I doubt any experienced explorer would have dared a sip of this water. To me, the mist of morbid mystery still surrounds the Amarina. Nevertheless, I still hold the towering fungi as the main suspects.