diff --git a/game/src/fx/AtmosphereTest.ts b/game/src/fx/AtmosphereTest.ts
new file mode 100644
index 0000000..13cf4db
--- /dev/null
+++ b/game/src/fx/AtmosphereTest.ts
@@ -0,0 +1,62 @@
+import Phaser from 'phaser';
+import { addLeaves, addReflection, blurForeground } from './atmosphere';
+import { StageState } from './atmosphereLayout';
+
+const BASE = 'assets/stages/rusty-creek/';
+/** rc-0-0 in draw order (stage.json), with each layer's scroll factor. */
+const LAYERS = [
+  { id: '01-distance', scroll: 0.2 },
+  { id: '03-bank', scroll: 1 },
+  { id: '02-supports', scroll: 1 },
+  { id: '04-water', scroll: 1 },
+  { id: '05-traversal', scroll: 1 },
+  { id: '06-near-rails', scroll: 1.1 },
+  { id: '07-foliage', scroll: 1.15 },
+];
+
+/**
+ * Dev only (#36 verification): the first Rusty Creek chunk with the blur, leaves and reflection.
+ * F10 opens it from the HUD; V shows and hides the atmosphere; A switches clean / anomaly leaves; arrows pan; Esc closes.
+ */
+export class AtmosphereTest extends Phaser.Scene {
+  private state: StageState = 'clean';
+  private leaves?: Phaser.GameObjects.Particles.ParticleEmitter;
+
+  constructor() { super('AtmosphereTest'); }
+
+  preload(): void {
+    for (const layer of LAYERS) this.load.image(`rc-test-${layer.id}`, `${BASE}${layer.id}-left.png`);
+  }
+
+  create(): void {
+    const images = LAYERS.map((l, i) => this.add.image(0, 0, `rc-test-${l.id}`).setOrigin(0).setScrollFactor(l.scroll, 1).setDepth(i));
+    const byId = (id: string) => images[LAYERS.findIndex((l) => l.id === id)];
+    const mirrored = images.filter((_, i) => LAYERS[i].id !== '04-water' && LAYERS[i].id !== '07-foliage');
+    const reflection = addReflection(byId('04-water'), mirrored);
+    const foliage = byId('07-foliage');
+    let on = true;
+    blurForeground(foliage);
+    this.leaves = addLeaves(this, this.state);
+    this.cameras.main.setBounds(0, 0, foliage.width, foliage.height);
+
+    const keys = this.input.keyboard;
+    keys?.on('keydown-V', () => {
+      on = !on;
+      reflection.setVisible(on);
+      this.leaves?.setVisible(on);
+      if (on) blurForeground(foliage); else foliage.preFX?.clear();
+    });
+    keys?.on('keydown-A', () => {
+      this.state = this.state === 'clean' ? 'anomaly' : 'clean';
+      this.leaves?.destroy();
+      this.leaves = addLeaves(this, this.state).setVisible(on);
+    });
+    keys?.on('keydown-ESC', () => this.scene.stop());
+    const arrows = keys?.createCursorKeys();
+    this.events.on(Phaser.Scenes.Events.UPDATE, (_t: number, delta: number) => {
+      if (arrows?.left.isDown) this.cameras.main.scrollX -= delta * 0.6;
+      if (arrows?.right.isDown) this.cameras.main.scrollX += delta * 0.6;
+    });
+    this.scene.bringToTop();
+  }
+}
diff --git a/game/src/fx/atmosphere.ts b/game/src/fx/atmosphere.ts
new file mode 100644
index 0000000..5c4b3cf
--- /dev/null
+++ b/game/src/fx/atmosphere.ts
@@ -0,0 +1,85 @@
+import Phaser from 'phaser';
+import { findWaterline, leafDrift, mirroredTop, rippleOffset, StageState } from './atmosphereLayout';
+
+/**
+ * Atmosphere over a stage chunk (#36, docs/04 layers 4, 7, 8): the foreground blur, falling leaves and the
+ * water reflection. Everything is built once; per frame only the reflection strips move a pixel or two.
+ */
+
+const LEAF_KEY = 'fx-leaf';
+const LEAF_COLOURS = [0xd9a03a, 0xc9622b, 0xe8c454, 0x9a4a24];
+const STRIP = 4;
+
+/** Softens the foreground layer (scroll 1.15–1.2) with a WebGL blur; returns false on the Canvas renderer. */
+export function blurForeground(layer: Phaser.GameObjects.Image, strength = 1.2): boolean {
+  if (!layer.preFX) return false;
+  layer.preFX.addBlur(1, 2, 2, strength);
+  return true;
+}
+
+/** Leaves drifting across the view at foreground parallax; they fall when clean and rise in the anomaly state. */
+export function addLeaves(scene: Phaser.Scene, state: StageState, scroll = 1.15): Phaser.GameObjects.Particles.ParticleEmitter {
+  if (!scene.textures.exists(LEAF_KEY)) {
+    const g = scene.make.graphics({}, false);
+    LEAF_COLOURS.forEach((c, i) => g.fillStyle(c).fillRect(i * 6 + 1, 0, 4, 3).fillRect(i * 6, 1, 6, 1));
+    g.generateTexture(LEAF_KEY, LEAF_COLOURS.length * 6, 3).destroy();
+    LEAF_COLOURS.forEach((_, i) => scene.textures.get(LEAF_KEY).add(i, 0, i * 6, 0, 6, 3));
+  }
+  const { width, height } = scene.scale;
+  const drift = leafDrift(state);
+  const emitter = scene.add.particles(0, 0, LEAF_KEY, {
+    frame: LEAF_COLOURS.map((_, i) => i),
+    x: { min: -40, max: width + 200 },
+    y: state === 'clean' ? -10 : height + 10,
+    speedX: { min: drift.speedX[0], max: drift.speedX[1] },
+    speedY: { min: drift.speedY[0], max: drift.speedY[1] },
+    rotate: { min: 0, max: 360 },
+    scale: { min: 2, max: 3.5 },
+    lifespan: 16_000,
+    frequency: 180,
+    advance: 12_000, // start with the view already full of leaves
+  }).setScrollFactor(0).setDepth(50);
+  // Screen-space emitter, nudged against the camera so the leaves pass faster than the scenery (parallax > 1).
+  const cam = scene.cameras.main;
+  let lastX = cam.scrollX;
+  const follow = () => {
+    const dx = (cam.scrollX - lastX) * scroll;
+    lastX = cam.scrollX;
+    if (dx) emitter.forEachAlive((p) => { p.x -= dx; }, undefined);
+  };
+  scene.events.on(Phaser.Scenes.Events.UPDATE, follow);
+  emitter.once(Phaser.GameObjects.Events.DESTROY, () => scene.events.off(Phaser.Scenes.Events.UPDATE, follow));
+  return emitter;
+}
+
+/**
+ * The water mirrors `layers` (docs/04: 1–6) about the waterline, masked to the water layer, with a ripple.
+ * The mirror is drawn once into a texture; the ripple moves horizontal strips of it.
+ */
+export function addReflection(water: Phaser.GameObjects.Image, layers: Phaser.GameObjects.Image[], alpha = 0.4): Phaser.GameObjects.Container {
+  const scene = water.scene;
+  const key = water.texture.key;
+  const waterline = findWaterline(water.width, water.height, (x, y) => scene.textures.getPixelAlpha(x, y, key) ?? 0);
+  const height = water.height - waterline;
+  const textureKey = `${key}-reflection`;
+  if (!scene.textures.exists(textureKey)) {
+    const rt = scene.make.renderTexture({ width: water.width, height }, false);
+    for (const layer of layers) {
+      const flipped = scene.make.image({ key: layer.texture.key, add: false }).setOrigin(0).setFlipY(true);
+      rt.draw(flipped, 0, mirroredTop(waterline, layer.height) - waterline);
+      flipped.destroy();
+    }
+    rt.saveTexture(textureKey);
+  }
+  const strips = Array.from({ length: Math.ceil(height / STRIP) }, (_, i) =>
+    scene.add.image(0, 0, textureKey).setOrigin(0).setCrop(0, i * STRIP, water.width, STRIP));
+  const container = scene.add.container(water.x, water.y + waterline, strips)
+    .setAlpha(alpha)
+    .setScrollFactor(water.scrollFactorX, water.scrollFactorY)
+    .setDepth(water.depth + 0.01);
+  container.setMask(water.createBitmapMask());
+  const ripple = (time: number) => strips.forEach((s, i) => { s.x = rippleOffset(i, time); });
+  scene.events.on(Phaser.Scenes.Events.UPDATE, ripple);
+  container.once(Phaser.GameObjects.Events.DESTROY, () => scene.events.off(Phaser.Scenes.Events.UPDATE, ripple));
+  return container;
+}
diff --git a/game/src/fx/atmosphereLayout.test.ts b/game/src/fx/atmosphereLayout.test.ts
new file mode 100644
index 0000000..fb8bd4a
--- /dev/null
+++ b/game/src/fx/atmosphereLayout.test.ts
@@ -0,0 +1,32 @@
+import { describe, expect, it } from 'vitest';
+import { findWaterline, leafDrift, mirroredTop, rippleOffset } from './atmosphereLayout';
+
+describe('the atmosphere layers', () => {
+  it('finds the first mostly-opaque row of the water layer, ignoring stray pixels above it', () => {
+    const alphaAt = (x: number, y: number) => (y >= 597 || (y === 100 && x === 0) ? 255 : 0);
+    expect(findWaterline(2160, 720, alphaAt)).toBe(597);
+    expect(findWaterline(100, 50, () => 0)).toBe(50);
+  });
+
+  it('mirrors a layer about the waterline', () => {
+    // A 720 px layer flipped and placed here maps row r to 2·596 − 1 − r.
+    const top = mirroredTop(596, 720);
+    expect(top).toBe(472);
+    const row = 100;
+    expect(top + (720 - 1 - row)).toBe(2 * 596 - 1 - row);
+  });
+
+  it('ripples by whole pixels within the amplitude, and neighbouring strips differ', () => {
+    for (let t = 0; t < 5000; t += 37) {
+      const o = rippleOffset(3, t, 2);
+      expect(Number.isInteger(o)).toBe(true);
+      expect(Math.abs(o)).toBeLessThanOrEqual(2);
+    }
+    expect([0, 1, 2, 3].map((i) => rippleOffset(i, 0, 2))).not.toEqual([0, 0, 0, 0]);
+  });
+
+  it('lets leaves fall in the clean state and rise in the anomaly state', () => {
+    expect(Math.min(...leafDrift('clean').speedY)).toBeGreaterThan(0);
+    expect(Math.max(...leafDrift('anomaly').speedY)).toBeLessThan(0);
+  });
+});
diff --git a/game/src/fx/atmosphereLayout.ts b/game/src/fx/atmosphereLayout.ts
new file mode 100644
index 0000000..68acde5
--- /dev/null
+++ b/game/src/fx/atmosphereLayout.ts
@@ -0,0 +1,51 @@
+/** Numbers for the atmosphere layers (docs/04: layers 4, 7, 8), kept pure so they are tested without Phaser. */
+
+export type StageState = 'clean' | 'anomaly';
+
+/**
+ * The first row where the water layer is mostly opaque: the reflection starts there.
+ * `alphaAt(x, y)` reads the layer's alpha (0–255); rows and columns are sampled every `step` px.
+ */
+export function findWaterline(width: number, height: number, alphaAt: (x: number, y: number) => number, step = 4, cover = 0.5): number {
+  for (let y = 0; y < height; y += step) {
+    let solid = 0;
+    let samples = 0;
+    for (let x = 0; x < width; x += step * 4) {
+      samples++;
+      if (alphaAt(x, y) > 128) solid++;
+    }
+    if (solid / samples >= cover) {
+      // Walk back up to the exact first solid row.
+      while (y > 0 && rowCover(width, y - 1, alphaAt, step * 4) >= cover) y--;
+      return y;
+    }
+  }
+  return height;
+}
+
+function rowCover(width: number, y: number, alphaAt: (x: number, y: number) => number, stride: number): number {
+  let solid = 0;
+  let samples = 0;
+  for (let x = 0; x < width; x += stride) {
+    samples++;
+    if (alphaAt(x, y) > 128) solid++;
+  }
+  return solid / samples;
+}
+
+/** Where a vertically flipped copy of a layer `height` px tall goes so it mirrors about `waterline`. */
+export function mirroredTop(waterline: number, height: number): number {
+  return 2 * waterline - height;
+}
+
+/** Ripple: each horizontal strip of the reflection sways sideways a few whole pixels, out of phase with its neighbours. */
+export function rippleOffset(strip: number, timeMs: number, amplitude = 2): number {
+  return Math.round(amplitude * Math.sin(timeMs / 420 + strip * 0.7));
+}
+
+/** Leaves fall and drift left in the clean state; in the anomaly state they drift upward (#36). */
+export function leafDrift(state: StageState): { speedX: [number, number]; speedY: [number, number] } {
+  return state === 'clean'
+    ? { speedX: [-60, -20], speedY: [25, 55] }
+    : { speedX: [-40, 10], speedY: [-55, -25] };
+}
diff --git a/game/src/scenes/registry.ts b/game/src/scenes/registry.ts
index dfd2cba..fe32f04 100644
--- a/game/src/scenes/registry.ts
+++ b/game/src/scenes/registry.ts
@@ -1,5 +1,6 @@
 import type Phaser from 'phaser';
 import { AnomalyTest } from '../fx/AnomalyTest';
+import { AtmosphereTest } from '../fx/AtmosphereTest';
 import { Crossing } from '../story/Crossing';
 import { Hud } from '../ui/Hud';
 import { Title } from '../ui/Title';
@@ -11,5 +12,5 @@ import { Title } from '../ui/Title';
 export const LANE_A_SCENES: Phaser.Types.Scenes.SceneType[] = [
   Hud, Crossing, Title,
   // Dev-only test scenes stay out of production builds.
-  ...(import.meta.env.DEV ? [AnomalyTest] : []),
+  ...(import.meta.env.DEV ? [AnomalyTest, AtmosphereTest] : []),
 ];
diff --git a/game/src/ui/Hud.ts b/game/src/ui/Hud.ts
index 0435932..aa2c16b 100644
--- a/game/src/ui/Hud.ts
+++ b/game/src/ui/Hud.ts
@@ -30,6 +30,10 @@ export class Hud extends Phaser.Scene {
     if (import.meta.env.DEV) this.input.keyboard?.on('keydown-F9', () => {
       if (!this.scene.isActive('AnomalyTest')) this.scene.launch('AnomalyTest');
     });
+    // Dev builds: F10 opens the atmosphere test chunk (#36 verification).
+    if (import.meta.env.DEV) this.input.keyboard?.on('keydown-F10', () => {
+      if (!this.scene.isActive('AtmosphereTest')) this.scene.launch('AtmosphereTest');
+    });
   }
 
   update(): void {