diff --git a/Shared/World.cs b/Shared/World.cs
index 05fbb2b..bed9048 100644
--- a/Shared/World.cs
+++ b/Shared/World.cs
@@ -11,10 +11,11 @@ namespace SemiColinGames {
     private TextureRef texture;
     private Rectangle textureSource;
 
-    public Tile(TextureRef texture, Rectangle textureSource, Rectangle position) {
+    public Tile(TextureRef texture, Rectangle textureSource, Rectangle position, bool isHazard) {
       Position = position;
       this.texture = texture;
       this.textureSource = textureSource;
+      IsHarmful = isHazard;
     }
 
     public Rectangle Position { get; private set; }
@@ -52,6 +53,8 @@ namespace SemiColinGames {
     }
 
     private List<Tile> ParseLayer(JToken layer) {
+      string layerName = layer.SelectToken("name").Value<string>();
+
       var tileList = new List<Tile>();
 
       int layerWidth = layer.SelectToken("gridCellsX").Value<int>();
@@ -76,7 +79,8 @@ namespace SemiColinGames {
         int y = textureIndex / textureWidth;
         Rectangle textureSource = new Rectangle(
             x * tileWidth, y * tileHeight, tileWidth, tileHeight);
-        tileList.Add(new Tile(Textures.Grassland, textureSource, position));
+        bool isHazard = layerName == "hazards";
+        tileList.Add(new Tile(Textures.Grassland, textureSource, position, isHazard));
       }
 
       return tileList;
@@ -99,9 +103,15 @@ namespace SemiColinGames {
       return (player, npcs.ToArray());
     }
 
+    static int CompareByX(Tile t1, Tile t2) {
+      return t1.Position.X.CompareTo(t2.Position.X);
+    }
+
     public World(string json) {
       JObject root = JObject.Parse(json);
 
+      List<Tile> hazardTiles = new List<Tile>();
+      List<Tile> obstacleTiles = new List<Tile>();
       List<Tile> decorationTiles = new List<Tile>();
       List<Tile> backgroundTiles = new List<Tile>();
       foreach (JToken layer in root.SelectToken("layers").Children()) {
@@ -112,23 +122,28 @@ namespace SemiColinGames {
           continue;
         }
         List<Tile> tileList = ParseLayer(layer);
-        if (layerName == "obstacles") {
-          tiles = tileList.ToArray();
+        if (layerName == "hazards") {
+          hazardTiles = tileList;
+        } else if (layerName == "obstacles") {
+          obstacleTiles = tileList;
         } else if (layerName == "decorations") {
           decorationTiles = tileList;
         } else if (layerName == "background") {
           backgroundTiles = tileList;
         }
       }
+      // Get all the obstacles into a single array, sorted by X.
+      obstacleTiles.AddRange(hazardTiles);
+      tiles = obstacleTiles.ToArray();
+      Array.Sort(tiles, CompareByX);
       // The background tiles are added before the rest of the decorations, so that they're drawn
       // in the back.
       backgroundTiles.AddRange(decorationTiles);
       decorations = backgroundTiles.ToArray();
       Debug.WriteLine("world size: {0}x{1}", gridWidth, gridHeight);
 
-      // Because we added tiles from left to right, the CollisionTargets are sorted by x-position.
-      // We maintain this invariant so that it's possible to efficiently find CollisionTargets that
-      // are nearby a given x-position.
+      // The obstacles are sorted by x-position. We maintain this invariant so that it's possible
+      // to efficiently find CollisionTargets that are nearby a given x-position.
       CollisionTargets = new AABB[tiles.Length + 2];
 
       // Add a synthetic collisionTarget on the left side of the world.