These Duskwalker are not as wise as they believe themselves to be. They had planned to cover their tracks by poisoning the water - in hopes that anyone who stumbled on these bodies would assume they had died from the contamination. They had no idea they were being watched. Now, it is left to us to clean up their mess. Here is a portion of the materials needed to cleanse these waters. You collect that portion, and I will collect the other half. Return them to me, and I will finish the cleansing.