There is a repeatable quest in Shadowprey Village in Desolace named Fish in a Bucket. You simply need to swim around the water off the coast of the Village and loot the Shellfish Traps to obtain Shellfish. Each 5 shellfish lets you hand in the quest for 55s. You only need level 25 (Preferably 30+) to do this.

As a druid, you can make 50g+ per hour if you are paying attention, and as a normal class, you can still get upwards of 20g+~/hr depending on how contested the area is.

I highly advise using Azure Silk Belt if you are doing this. Also, swim into the bubble fissures to reset your breath!

Enjoy