Water Chest

Yes, early, and mostly for one item. The Water Walking Boots are the rarest thing in the pool and comfortably the most useful, since they remove the biggest reason lakes and coastline slow you down. The Trident is a fair pre-Hardmode weapon, and a Flipper or Breathing Reed pays for itself during the same trip you loot it because it makes clearing the rest of the sea floor much less painful. Once you own boots and a Flipper, further chests are mostly duplicates.

The Ocean is the obvious place, but any large enough body of water can hold one: underground lakes, surface ponds, even the occasional lake on a floating island. The odds do not shift with the biome. Chests generated in Ocean caves are the exception worth knowing, since every headline item there is equally likely instead of weighted toward one.

• In a Not the Bees world the water is replaced with honey and these chests generate in it anyway. That is the only time you will find one outside water.
• Celebration Mk 10 worlds tilt the odds heavily toward the Water Walking Boots at everything else's expense, which is the version of this chest actually worth farming.