Is it possible that every body of water in the entire world be guarded by a Maia of Ulmo? This is just a hypothesis, but it can bring upon some more thoughts. For example, Ithilduin was the river that flows by Minas Ithil. After its fall it became Minas Morgul, and the river Morgulduin. It was said that in Minas Morgul the minds of living Men would turn to madness. Could it be that the guardian Maia of Ithilduin become corrupted and fall into evil and with its magic and spells weave about this change?