diff --git a/packages/web/src/App.svelte b/packages/web/src/App.svelte
index 9f5e661..ac61596 100644
--- a/packages/web/src/App.svelte
+++ b/packages/web/src/App.svelte
@@ -512,7 +512,7 @@
     "destroy-wall": "click a wall or door to destroy it",
     "illusion-wall": "click an open corridor line for the false wall",
     "wall-of-fire": "click a corridor line for the fire",
-    "waterwall": "click a corridor line — the wave collapses at once",
+    "waterwall": "click a corridor line, or a slime to wash it away — the wave collapses at once",
     "pick-lock": "click a locked door",
     "master-key": "click a locked door — or Display it once and walk through every lock",
     "jam-lock": "click a door to jam its lock solid",
@@ -1050,10 +1050,25 @@
       clearSelection();
       return;
     }
+    // "A WATERWALL ... will wash the slime away": the card wants a corridor
+    // line, so a tap on the slime itself picks the square's face nearest the
+    // caster and the wave breaks against the gel. Sight is still the engine's
+    // to judge.
+    if (selectedCard?.cardId === "waterwall" && filled === "slime") {
+      dispatch(withMods({
+        type: "cast", instanceId: selectedCard.instanceId,
+        target: { kind: "edge", cell, side: slimeFace(view.board, cell, me.position) },
+      }));
+      clearSelection();
+      return;
+    }
     // A card in hand is aimed, not walked with: a tap on a bare square
     // while holding one is a miss, never a stride into whatever is there.
     if (selectedCard) {
-      net.flash(`${cardDef(selectedCard.cardId).name} is aimed by tapping a wizard, a creature, a bush, or a slime — put the card down to walk`);
+      const name = cardDef(selectedCard.cardId).name;
+      net.flash(EDGE_CARDS.has(selectedCard.cardId)
+        ? `${name} is aimed at a line between squares: ${EDGE_HINTS[selectedCard.cardId] ?? "tap a lit line"}`
+        : `${name} is aimed by tapping a wizard, a creature, a bush, or a slime — put the card down to walk`);
       return;
     }
     // A cell click is a move if the cell is one legal step away (the server
@@ -1191,6 +1206,17 @@
     }
   }
 
+  /** The face of a slime square a waterwall breaks against when the square
+   * itself is tapped. The wave washes two squares out from both sides of
+   * its line, so the line runs across the caster's approach rather than
+   * along it: a tap means "wash the slime", not "wash me". Walls and the
+   * board's rim are never chosen while another face is free. */
+  function slimeFace(board: GameView["board"], slime: { x: number; y: number }, from: { x: number; y: number }): Side {
+    const across: Side[] = Math.abs(from.x - slime.x) >= Math.abs(from.y - slime.y) ? ["N", "S", "W", "E"] : ["W", "E", "N", "S"];
+    const free = across.filter((side) => { const t = stepTarget(board, slime, side); return t.kind !== "blocked" || t.by !== "wall"; });
+    return free[0] ?? across[0]!;
+  }
+
   function clickEdge(cell: { x: number; y: number }, side: Side) {
     if (punchWallMode) {
       dispatch({ type: "punchWall", cell, side });