Agata needs you to collect 10 Tillage moon rocks from the waters around the Tillage patch water area ( -726, -944, -185 ) /waypoint -726, -944, -185
Return to Agata ( -809, -917, -398 ) /waypoint -809, -917, -398 with the rocks.
The rocks are "clicky" items and do not require any harvesting skill to collect. They are spread out within the same body of water, so be prepared to dive under the water many times to collect all of them. If you have a Totem of the Otter or water breathing, use it before you begin diving for rocks.
None of the creatures in the water are aggressive (no aggro), so the area you need to dive in is safe at any level.