Using a shovel enchanted with Fortune on sand in an ocean or river biome has a chance to yield sunken treasure. This can include rare loot like sponges and a Message in a Bottle.

Rewards

In Java Edition, each sunken treasure contains 1 item stacks, with the following distribution:

Item Stack Size [FN 1] Weight [FN 2] Chance [FN 3] Avg.
per chest
[FN 4]
Avg. # chests
to search
[FN 5]
 Bone 11729999917.3%0.1735.8
File:ParallelItemSprite message-in-a-bottle.pngMessage In A Bottle 11152999911.5%0.1158.7
 Prismarine Crystals 157699995.8%0.05817.4
File:ParallelItemSprite waders.pngWaders 130099993.0%0.03033.3
 Bottle o' Enchanting 128899992.9%0.02934.7
 Gold Ingot 128899992.9%0.02934.7
 Leather Boots 125099992.5%0.02540.0
File:ParallelItemSprite treasure-chest.pngTreasure Chest 15899990.6%0.006172.4
  1. The size of stacks (or for unstackable items, number) of this item on any given roll.
  2. The weight of this item relative to other items in the pool.
  3. The odds of finding any of this item in a single chest.
  4. The number of items expected per chest, averaged over a large number of chests.
  5. The average number of chests the player should expect to search to find any of this item.