diff --git a/docs/landscape.html b/docs/landscape.html
--- a/docs/landscape.html
+++ b/docs/landscape.html
@@ -759,6 +759,7 @@
    <td valign=top nowrap>&nbsp;</td>
    <td>
     <ul>
+     <li>m1 bits 6..5: water class (sea or land)</li>
      <li>m1 bits 4..0: <a href="#OwnershipInfo">owner</a> (normally <tt>10</tt>)</li>
      <li>m2 bits 8..6: ground
       <table>
diff --git a/docs/landscape_grid.html b/docs/landscape_grid.html
--- a/docs/landscape_grid.html
+++ b/docs/landscape_grid.html
@@ -194,7 +194,7 @@ the array so you can quickly see what is
       <td class="caption">trees</td>
       <td class="bits">XXXX XXXX</td>
       <td class="bits">XXXX XXXX</td>
-      <td class="bits"><span class="free">OOO</span><span class="option">~ ~~~~</span></td>
+      <td class="bits"><span class="free">O</span>XX<span class="option">~ ~~~~</span></td>
       <td class="bits"><span class="free">OOOO OOO</span>X XXXX XXXX</td>
       <td class="bits"><span class="option">~~</span>XX XXXX</td>
       <td class="bits"><span class="free">OOOO OOOO</span></td>
diff --git a/src/tree_map.h b/src/tree_map.h
--- a/src/tree_map.h
+++ b/src/tree_map.h
@@ -13,6 +13,7 @@
 #define TREE_MAP_H
 
 #include "tile_map.h"
+#include "water_map.h"
 
 /**
  * List of tree types along all landscape types.
@@ -133,6 +134,7 @@ static inline void SetTreeGroundDensity(
 	assert(IsTileType(t, MP_TREES)); // XXX incomplete
 	SB(_m[t].m2, 4, 2, d);
 	SB(_m[t].m2, 6, 3, g);
+	SetWaterClass(t, g == TREE_GROUND_SHORE ? WATER_CLASS_SEA : WATER_CLASS_INVALID);
 }
 
 /**
diff --git a/src/water_map.h b/src/water_map.h
--- a/src/water_map.h
+++ b/src/water_map.h
@@ -94,7 +94,7 @@ static inline WaterTileType GetWaterTile
  */
 static inline bool HasTileWaterClass(TileIndex t)
 {
-	return IsTileType(t, MP_WATER) || IsTileType(t, MP_STATION) || IsTileType(t, MP_INDUSTRY) || IsTileType(t, MP_OBJECT);
+	return IsTileType(t, MP_WATER) || IsTileType(t, MP_STATION) || IsTileType(t, MP_INDUSTRY) || IsTileType(t, MP_OBJECT) || IsTileType(t, MP_TREES);
 }
 
 /**
@@ -204,7 +204,7 @@ static inline bool IsCoast(TileIndex t)
  */
 static inline bool IsCoastTile(TileIndex t)
 {
-	return IsTileType(t, MP_WATER) && IsCoast(t);
+	return (IsTileType(t, MP_WATER) && IsCoast(t)) || (IsTileType(t, MP_TREES) && GetWaterClass(t) != WATER_CLASS_INVALID);
 }
 
 /**