diff --git a/doc/fixes3-7-0.txt b/doc/fixes3-7-0.txt
index 630ae1e6b..7164fea35 100644
--- a/doc/fixes3-7-0.txt
+++ b/doc/fixes3-7-0.txt
@@ -1282,6 +1282,7 @@ save files created with SCORE_ON_BOTL disabled were erroneously being rejected
 	if the program was rebuilt with it enabled and vice versa
 avoid "It suddenly appears!" if a monster with the STRAT_APPEARMSG attribute
 	is seen to teleport away then not seen at its destination
+avoid boulder-on/in-water sanity_check warnings on the Plane of Water
 
 curses: 'msg_window' option wasn't functional for curses unless the binary
 	also included tty support
diff --git a/src/do.c b/src/do.c
index 172a4d3cd..7c6018f00 100644
--- a/src/do.c
+++ b/src/do.c
@@ -43,18 +43,23 @@ dodrop(void)
  * it's gone for good...  If the destination is not a pool, returns FALSE.
  */
 boolean
-boulder_hits_pool(struct obj *otmp, coordxy rx, coordxy ry, boolean pushing)
+boulder_hits_pool(
+    struct obj *otmp,
+    coordxy rx, coordxy ry,
+    boolean pushing)
 {
     if (!otmp || otmp->otyp != BOULDER) {
         impossible("Not a boulder?");
-    } else if (!Is_waterlevel(&u.uz) && is_pool_or_lava(rx, ry)) {
+    } else if (is_pool_or_lava(rx, ry)) {
         boolean lava = is_lava(rx, ry), fills_up;
         const char *what = waterbody_name(rx, ry);
         schar ltyp = levl[rx][ry].typ;
         int chance = rn2(10); /* water: 90%; lava: 10% */
         struct monst *mtmp;
 
-        fills_up = lava ? chance == 0 : chance != 0;
+        fills_up = Is_waterlevel(&u.uz) ? FALSE
+                   : (ltyp == WATER) ? (chance < 5) /* wall of water */
+                     : lava ? (chance == 0) : (chance != 0);
 
         if (fills_up) {
             struct trap *ttmp = t_at(rx, ry);
@@ -62,9 +67,9 @@ boulder_hits_pool(struct obj *otmp, coordxy rx, coordxy ry, boolean pushing)
             if (ltyp == DRAWBRIDGE_UP) {
                 levl[rx][ry].drawbridgemask &= ~DB_UNDER; /* clear lava */
                 levl[rx][ry].drawbridgemask |= DB_FLOOR;
-            } else
+            } else {
                 levl[rx][ry].typ = ROOM, levl[rx][ry].flags = 0;
-
+            }
             /* 3.7: normally DEADMONSTER() is used when traversing the fmon
                list--dead monsters usually aren't still at specific map
                locations; however, if ice melts causing a giant to drown,
@@ -100,8 +105,9 @@ boulder_hits_pool(struct obj *otmp, coordxy rx, coordxy ry, boolean pushing)
                     There("is a large splash as %s %s the %s.",
                           the(xname(otmp)), fills_up ? "fills" : "falls into",
                           what);
-                } else if (!Deaf)
+                } else if (!Deaf) {
                     You_hear("a%s splash.", lava ? " sizzling" : "");
+                }
                 wake_nearto(rx, ry, 40);
             }
 
@@ -112,6 +118,7 @@ boulder_hits_pool(struct obj *otmp, coordxy rx, coordxy ry, boolean pushing)
                 You("find yourself on dry land again!");
             } else if (lava && next2u(rx, ry)) {
                 int dmg;
+
                 You("are hit by molten %s%c",
                     hliquid("lava"), Fire_resistance ? '.' : '!');
                 burn_away_slime();