Possible Clues:

• Area between banks
• What's found at the end of Davy Jones' locker underneath the flower?
• Channel bottom
• Don's wet bottom?
• Flower in the garden from the lowest part of The Shannon
• It makes Mississippi mud?
• Flower in the garden is found in the lowest area of The Congo
• Dredged area, maybe
• Something dynamic, perhaps, in horribly dire wet bottom?
• At the bottom of the Liffey with Shannon for support