Entrances to the Lost River can be found in both Blood Kelp Zones and in the Deep Grand Reef. The Cyclops is able to enter the Lost River through the Deep Grand Reef and Northern Blood Kelp Zone. The Cyclops can traverse the whole way into the Inactive Lava Zone.
The Lost River is generally gloomy and foggy, possessing a distinct greenish water tint that is mostly illuminated by the acidic brine pools as well as an eerie atmosphere with the occasional Ghostray cry. These pools cover almost all of the lower portions of the caverns. The green brine found throughout most of the cave system will harm the player, but the blue brine found within the Tree Cove is harmless.
Spoiler alert: The following section contains story related material.
The Disease Research Facility is located in the Lost River, inside a cavern, with its opening in the Junction.
The Lost River is composed of six distinct areas:
The Bone Fields is a vast cavern within the Lost River, where a colossal skeleton of an unknown fauna can be seen laying, giving the Bone Fields it's name. It connects to the first Blood Kelp Zone, through passages, each of them having its own flora and particular landscape, as well as the Ghost Canyon. It also has its own cave system, the Bone Fields Caves.
The Lost River Corridor is the area connecting the Bone Fields and the Blood Kelp Trench. It is mainly characterised by Crabsquids, and obscure rock structures otherwise known as 'Slime Pillars'. Gel Sacks and Aluminium Oxide Crystals can be found scattered around the edge of the brine stream.
The Ghost Canyon is a huge passage featuring multiple caves and tunnels branching out from one main canyon. It connects to the Bone Fields from the south. Numerous roots and luminescent-tipped branches litter the sides and bottom of the brine-filled trenches.
A Precursor Cache that was set up to study a skeleton can be found in this area.
A large chamber that leads from the main entrance of the Lost River (located in the second Blood Kelp Zone). This area is filled with whitish glowing flora on the sea floor and dark brown, bioluminescent giant Ghost Trees, and is also the starting point of the brine river. There is steep drop off at the back end of the Forest, with a long brinefall, that leads to the Junction. From there, the player can either go straight forward into the Bone Fields, or turn right to enter the Tree Cove. Brinefalls of various sizes are present, and a smaller version of the skull found in the Bone Fields can be found here.
A Precursor Cache is present in this area, serving as a warp gate to the Primary Containment Facility.
The Tree Cove is a large cavern within the Lost River. The brine river forms a large lake there, with the luminous Giant Cove Tree in its center. However, the color of the brine is a bright blue, compared to the green brine of the other sections of the Lost River. One end opens to the north tunnel leading to the Junction, and the other, a corridor, to the Inactive Lava Zone. Roots and branches grow scattered on the brine-lakes and numerous Ghostrays inhabit the chamber.
The Junction is characterised by a large plateau surrounded by a ring of brine. At the top of the plateau are several smokers, and a few glowing blobs. A Sea Dragon Leviathan skeleton can be found on a small, flat platform in this area, next to a few white smokers. A naturally formed bridge connects the plateau to the northern side of the cavern, towards the Ghost Forest. Brinefalls from the north and south flow into the brine here, which contains some ghost trees and roots. The Junction connects to the Bone Fields to the south, the Ghost Forest to the north, the Disease Research Facility's cavern to the east, and the Tree Cove to the west. Precursor objects will be added to the Junction, as a means to grab player's attention to prevent them from missing the Disease Research Facility. 
Lost River Concept Art
For a more complete gallery, visit Lost River/Gallery.
- Like other segmented biomes (such as the Inactive Lava Zone), the Lost River's technical data divides it into the LostRiver_TreeCove, LostRiver_BonesField and LostRiver_BonesField again for the Ghost Canyon (this aids the AI in deciding music tracks, random events and creature behaviour).
- The acid damage from the brine may be possible implementation/reference to the "Pillars of Silence" concept art, where enormous jets of acid dot an alien seabed.
- The game also considers the actual brine to be a biome. It is labelled LostRiver_BonesField_Lake.
- The Ghost Forest was called the "Ghost Trees Chamber" before the Bones Update.
- ↑ https://trello.com/c/nvYmZ94J/6278-add-precursor-architecture-and-lighting-to-lost-river-base-chamber-entranceway-to-draw-players-attention
- ↑ http://unknownworlds.com/subnautica/bones-update/ Dated October 27, 2016.