Structures
Four NauTec structures generate in the oceans, each worth a visit early on.
All four generate in any ocean biome, including the four NauTec oceans, only where the ground is below sea level. None of them generate near an ocean monument.
An 
Eye of the Sea points the way to the nearest one of each kind, and to vanilla ocean ruins and monuments. See Eye of the Sea.
Ocean Ruins
A small arch of dark prismarine standing on the ocean floor, built from Chiseled Dark Prismarine, Dark Prismarine Pillars and dark prismarine slabs.
What to take:
- The
Aquatic Catalyst seated in the arch. Mine it and it drops as an item, so you get a catalyst before you can craft one. - A
Rusty Crate buried in the gravel at the foot of the arch. Break it to carry it away with its loot inside, then clean it in Etching Acid. - Suspicious Gravel mixed into that gravel. Brush it for gold nuggets, prismarine, Prismarine Laser Relays, a
Burnt Coil or an 
Atlantic Gold Nugget.
Crystal Geodes
Hollow rooms buried under the ocean floor. There are two kinds: a stone geode with its floor between y -10 and 30, and a deepslate geode with its floor between y -59 and -25. Both always have at least 4 blocks of rock above them, so under a deep seabed they sit lower. Nothing marks them on the surface. /locate and the Eye of the Sea point at the middle of the room.
In the middle stands a Prismarine Crystal inside scaffolding. It is the only natural source of a purity 3.0 beam, and it stays where it generated, so the geode is where you do high purity Item Transformation until you have other options. The crystal already has the open gap under it that the setup needs: one block in a stone geode, two in a deepslate geode.
Around it you will find:
- Barrels holding Rusty Gears, Aquarine Steel Compound,
Brown Polymer, 
Pressurized Air Bottles, prismarine and gold nuggets. - Crates holding Burnt Coils, Brown Polymer, Cast Iron Ingots, Prismarine Crystals, iron and Aquarine Steel Compound.
- Rusty Crates, about half of all the crates, holding better salvage: Ancient Valves, Rusty Gears, Burnt Coils, Atlantic Gold Nuggets, Aquarine Steel Ingots and sometimes a Heart of the Sea.
- A crafting table, a lectern, decorated pots and a small pool of salt water.
Crates open like a chest, but the rusty ones need etching first. See Crates and Etching.
Tip: an Aquarine Steel Pickaxe with its ability on can chip Prismarine Crystal Shards off the crystal, but every hit has a one in four chance to shatter it for good. Set up your transformations before you start chipping.
Underwater Gateways
A small platform of Polished Prismarine with a Dark Prismarine Pillar at each corner and a 
Gateway in the middle. The Gateway grows its full ring the first time the chunk loads. They are much rarer than ruins and geodes.
Each one is half of a pair with its own address. The first trip through it builds the other half about 1,500 blocks away in another ocean. See Gateway for how travel works.
Sunken Research Outposts
An abandoned research station on the floor of deep water, at least twelve blocks down. A domed hub of copper and cast iron with a skylight, joined by short corridors to three modules: a lab, a storage room and a power room. The whole station is flooded, the walls are holed, and seagrass has grown through the floor. Drowned spawn inside.
What to take:
- A Research Log on the lectern in the hub. There are four, each a few pages from the crew about the vents, the glowing caves, the trench and the gateways.
- Chests and a barrel with lab supplies: Petri Dishes, Glass Vials, Air Bottles, Aquarine Steel Compound, salvage parts, and now and then a submarine module, a
Diving Helmet or a Heart of the Sea. - Rusty Crates in the hub and the storage room.
- The
Pressure Hatch in the hub's doorway. Mine it with a pickaxe and it is yours, see Underwater Bases.
They are rarer than the ruins, and they only generate where the sea floor is fairly flat.
Vanilla Structures
Shipwrecks, ocean ruins, warm ocean ruin sand and buried treasure also hold NauTec loot. Salvage lists what turns up where.