Holding back the tide walls is not an easy task, even using the Tidestone. The ebb and flow of the magical energies in the area are too inconsistent.
We need to shore up our magical reserves, which requires mana batteries, if you will. The befouled elementals along the canal here are created with exactly the elemental cores we need.
The goal is two fold. Clearing out the befouled elementals, before their corruption spreads, but also retrieving their cores, so we can keep the water at bay.