How to Find and Use Tectonic's Underground Rivers

What Underground Rivers Are

Tectonic generates underground rivers where surface rivers meet cave systems, carving water channels through stone below the surface. They are not marked on maps, so you find them by caving or by mining toward the sound of flowing water. Because they connect to surface rivers, following a river downstream and digging into its banks is often the fastest way to break into one.

Exploring Them Safely

• Bring a water breathing potion or turtle shell if you plan to swim long stretches.
• Carry torches and a bed; underground rivers can run for long distances and you may not surface quickly.
• Watch for currents — flowing water can push you into drops or into mob-filled caverns.
• Mark your entry point with torches or a distinctive block so you can find your way back.

Underground rivers are useful for two things: fast, safe travel between distant cave systems, and resource gathering. The water erodes surrounding stone, often exposing ores along the banks. If you build a base near one, you can use it as a natural moat or a hidden water elevator shaft. Just be aware that the open water and darkness make them prime spawning grounds for drowned and other hostile mobs, so light the banks thoroughly before settling in.