diff --git a/data/json/overmap/map_extras.json b/data/json/overmap/map_extras.json
index c33ede5524668..290de83ed93b9 100644
--- a/data/json/overmap/map_extras.json
+++ b/data/json/overmap/map_extras.json
@@ -348,7 +348,7 @@
     "sym": "p",
     "color": "blue",
     "autonote": true,
-    "flags": [ "CLASSIC" ]
+    "flags": [ "CLASSIC", "WATER" ]
   },
   {
     "id": "mx_pond_forest",
@@ -357,7 +357,7 @@
     "description": "Small basin is here.",
     "generator": { "generator_method": "update_mapgen", "generator_id": "mx_pond_forest" },
     "min_max_zlevel": [ 0, 0 ],
-    "flags": [ "CLASSIC" ]
+    "flags": [ "CLASSIC", "WATER" ]
   },
   {
     "id": "mx_pond_forest_2",
@@ -365,7 +365,7 @@
     "copy-from": "mx_pond_forest",
     "generator": { "generator_method": "update_mapgen", "generator_id": "mx_pond_forest_2" },
     "min_max_zlevel": [ 0, 0 ],
-    "flags": [ "CLASSIC" ]
+    "flags": [ "CLASSIC", "WATER" ]
   },
   {
     "id": "mx_pond_swamp",
@@ -374,7 +374,7 @@
     "description": "Small bog is here.",
     "generator": { "generator_method": "update_mapgen", "generator_id": "mx_pond_swamp" },
     "min_max_zlevel": [ 0, 0 ],
-    "flags": [ "CLASSIC" ]
+    "flags": [ "CLASSIC", "WATER" ]
   },
   {
     "id": "mx_pond_swamp_2",
@@ -382,7 +382,7 @@
     "copy-from": "mx_pond_swamp",
     "generator": { "generator_method": "update_mapgen", "generator_id": "mx_pond_swamp_2" },
     "min_max_zlevel": [ 0, 0 ],
-    "flags": [ "CLASSIC" ]
+    "flags": [ "CLASSIC", "WATER" ]
   },
   {
     "id": "mx_trees",
diff --git a/data/json/overmap/overmap_special/specials.json b/data/json/overmap/overmap_special/specials.json
index b38bfb1ef162d..e1e09e4e25b39 100644
--- a/data/json/overmap/overmap_special/specials.json
+++ b/data/json/overmap/overmap_special/specials.json
@@ -240,7 +240,7 @@
     "locations": [ "land" ],
     "city_distance": [ 4, -1 ],
     "occurrences": [ 0, 1 ],
-    "flags": [ "CLASSIC", "WILDERNESS" ]
+    "flags": [ "CLASSIC", "WILDERNESS", "WATER" ]
   },
   {
     "type": "overmap_special",
diff --git a/data/json/overmap/overmap_terrain/overmap_terrain.json b/data/json/overmap/overmap_terrain/overmap_terrain.json
index 1a00dec294eae..5c49ed398854c 100644
--- a/data/json/overmap/overmap_terrain/overmap_terrain.json
+++ b/data/json/overmap/overmap_terrain/overmap_terrain.json
@@ -677,7 +677,8 @@
     "sym": ".",
     "color": "blue",
     "see_cost": "none",
-    "mondensity": 2
+    "mondensity": 2,
+    "flags": [ "WATER" ]
   },
   {
     "type": "overmap_terrain",
@@ -687,7 +688,8 @@
     "sym": ".",
     "color": "light_blue",
     "see_cost": "none",
-    "mondensity": 1
+    "mondensity": 1,
+    "flags": [ "WATER" ]
   },
   {
     "type": "overmap_terrain",