diff --git a/mods/MAPGEN/mcl_biomes/init.lua b/mods/MAPGEN/mcl_biomes/init.lua
index e065f619c..03f3c11fc 100644
--- a/mods/MAPGEN/mcl_biomes/init.lua
+++ b/mods/MAPGEN/mcl_biomes/init.lua
@@ -48,10 +48,19 @@ local function register_biomes()
 	In MT, any biome can occour in any terrain, so these variants are implied and are therefore
 	not explicitly implmented in MCL2. “M” variants are only included if they have another unique feature,
 	such as a different land cover.
-	In MCL2, the MC Overworld biomes are usually split in two or more parts (stacked by height), at least
-	a land part and an ocean part. Sometimes there's a beach/shore part as well.
+	In MCL2, the MC Overworld biomes are split in multiple more parts (stacked by height):
+	* The main part, this represents the land. It begins at around sea level and usually goes all the way up
+	* _ocean: For the area covered by ocean water. The y_max may vary for various beach effects.
+	          Has sand or dirt as floor.
+	* _deep_ocean: Like _ocean, but deeper and has gravel as floor
+	* _underground:
+	* Other modifiers: Some complex biomes require more layers to improve the landscape.
 
-	The ocean biomes correspond to the MC Ocean biome.
+	The following naming conventions apply:
+	* The land biome name is equal to the MC biome name (in camel case)
+	* Height modifiers and sub-biomes are appended with underscores and in lowercase. Example: “_ocean”
+	* Non-MC biomes are written in lowercase
+	* MC dimension biomes are named after their MC dimension
 
 	Intentionally missing biomes:
 	* River (generated by valleys and v7)
@@ -67,14 +76,8 @@ local function register_biomes()
 	* Mesa Plateau F M
 	* Extreme Hills Edge
 
-	The following naming conventions apply:
-	* The land biome name is equal to the MC biome name (in camel case)
-	* Height modifiers and sub-biomes are appended with underscores and in lowercase. Example: “_ocean”
-	* Non-MC biomes are written in lowercase
-	* MC dimension biomes are named after their MC dimension
-
 	TODO:
-	* Better beaches (varying height, beach and cold beach as biomes)
+	* Better beaches
 	* Extreme Hills+ M
 	* Desert M
 
@@ -85,7 +88,42 @@ local function register_biomes()
 
 	]]
 
-	local OCEAN_MIN = mcl_vars.mg_overworld_min
+	-- List of Overworld biomes without modifiers.
+	-- IMPORTANT: Don't forget to add new Overworld biomes to this list!
+	local overworld_biomes = {
+		"IcePlains",
+		"IcePlainsSpikes",
+		"ColdTaiga",
+		"ExtremeHills",
+		"ExtremeHillsM",
+		"ExtremeHills+",
+		"Taiga",
+		"MegaTaiga",
+		"MegaSpruceTaiga",
+		"StoneBeach",
+		"Plains",
+		"SunflowerPlains",
+		"Forest",
+		"FlowerForest",
+		"BirchForest",
+		"BirchForestM",
+		"RoofedForest",
+		"Swampland",
+		"Jungle",
+		"JungleM",
+		"JungleEdge",
+		"JungleEdgeM",
+		"MushroomIsland",
+		"Desert",
+		"Savanna",
+		"SavannaM",
+		"Mesa",
+		"MesaPlateauF",
+	}
+
+	local OCEAN_MIN = -15
+	local DEEP_OCEAN_MAX = OCEAN_MIN - 1
+	local DEEP_OCEAN_MIN = -31
 
 	-- Ice Plains Spikes (rare)
 	minetest.register_biome({
@@ -1112,6 +1150,36 @@ local function register_biomes()
 		heat_point = 50,
 	})
 
+	-- Add deep ocean and underground biomes automatically.
+	for i=1, #overworld_biomes do
+		local biome = overworld_biomes[i]
+
+		-- Deep Ocean: Has gravel floor
+		minetest.register_biome({
+			name = biome .. "_deep_ocean",
+			heat_point = minetest.registered_biomes[biome].heat_point,
+			humidity_point = minetest.registered_biomes[biome].humidity_point,
+			y_min = DEEP_OCEAN_MIN,
+			y_max = DEEP_OCEAN_MAX,
+			node_top = "mcl_core:gravel",
+			depth_top = 1,
+			node_filler = "mcl_core:gravel",
+			depth_filler = 2,
+			node_riverbed = "mcl_core:gravel",
+			depth_riverbed = 2,
+		})
+
+		-- Underground biomes are used to identify the underground and to prevent nodes from the surface
+		-- (sand, dirt) from leaking into the underground.
+		minetest.register_biome({
+			name = biome .. "_underground",
+			heat_point = minetest.registered_biomes[biome].heat_point,
+			humidity_point = minetest.registered_biomes[biome].humidity_point,
+			y_min = mcl_vars.mg_overworld_min,
+			y_max = DEEP_OCEAN_MIN - 1,
+		})
+
+	end
 end
 
 -- Register biomes of non-Overworld biomes
diff --git a/mods/MAPGEN/mcl_mapgen_core/init.lua b/mods/MAPGEN/mcl_mapgen_core/init.lua
index 8ce521f1f..8cc66e709 100644
--- a/mods/MAPGEN/mcl_mapgen_core/init.lua
+++ b/mods/MAPGEN/mcl_mapgen_core/init.lua
@@ -439,7 +439,7 @@ else
 		clust_size     = 1,
 		y_min          = mcl_util.layer_to_y(4),
 		y_max          = mcl_util.layer_to_y(32),
-		biomes         = { "ExtremeHills", "ExtremeHills_beach", "ExtremeHills_ocean", },
+		biomes         = { "ExtremeHills", "ExtremeHills_beach", "ExtremeHills_ocean", "ExtremeHills_deep_ocean", "ExtremeHills_underground" },
 	})
 end
 
@@ -645,7 +645,7 @@ minetest.register_ore({
 	clust_size     = 2,
 	y_min          = mcl_vars.mg_overworld_min,
 	y_max          = mcl_util.layer_to_y(61),
-	biomes         = { "ExtremeHills", "ExtremeHills_beach", "ExtremeHills_ocean", },
+	biomes         = { "ExtremeHills", "ExtremeHills_beach", "ExtremeHills_ocean", "ExtremeHills_deep_ocean", "ExtremeHills_underground" },
 })
 
 
@@ -1173,8 +1173,8 @@ local function generate_structures(minp, maxp, seed, biomemap)
 						if ground_y <= 0 and nn == "mcl_core:dirt" then
 							local prob = minecraft_chunk_probability(48, minp, maxp)
 
-							local swampland = minetest.get_biome_id("JungleEdge")
-							local swampland_shore = minetest.get_biome_id("JungleEdge_ocean")
+							local swampland = minetest.get_biome_id("Swampland")
+							local swampland_shore = minetest.get_biome_id("Swampland_shore")
 
 							-- Where do witches live?