diff --git a/public/tide-pool-world.js b/public/tide-pool-world.js
index a57c71e..c0ee361 100644
--- a/public/tide-pool-world.js
+++ b/public/tide-pool-world.js
@@ -36,7 +36,11 @@ const distance = (a, b) => Math.hypot(a.x - b.x, a.z - b.z);
 const TIDE_PHASE = -1.1;
 export const tideOf = t => .5 + .5 * Math.sin(t / TIDE_PERIOD * Math.PI * 2 + TIDE_PHASE);
 export const tideRising = t => Math.cos(t / TIDE_PERIOD * Math.PI * 2 + TIDE_PHASE) > 0;
-export const waterLevel = world => lerp(TIDE_LOW, TIDE_HIGH, tideOf(world.time));
+// Springs and neaps: the range of the tide swells and shrinks over twenty minutes, so some low waters lay the shelf bare
+// and some high waters flood it deep, while at neaps the water barely moves. The shelf opens at springs.
+export const SPRING_PERIOD = 1200;
+export const tideRange = t => 1 + .32 * Math.cos(t / SPRING_PERIOD * Math.PI * 2);
+export const waterLevel = world => (TIDE_LOW + TIDE_HIGH) / 2 + (tideOf(world.time) - .5) * (TIDE_HIGH - TIDE_LOW) * tideRange(world.time);
 export const daylight = world => {
   const s = Math.sin(world.time / DAY_PERIOD * Math.PI * 2 + .45);
   const t = clamp((s + .25) / .6, 0, 1);
diff --git a/public/tide-pool.js b/public/tide-pool.js
index ee1ee46..306c464 100644
--- a/public/tide-pool.js
+++ b/public/tide-pool.js
@@ -1,7 +1,7 @@
 import {
   createWorld, advanceWorld, offerObject, SPECIES, SPECIES_ORDER, CELL, COLS, ROWS, X0, Z0, X1, Z1, START_POOL, waterLevel, daylight,
   heightAt, surfaceAt, depthAt, onShelf, bodyAt, tideOf, tideRising, label, goalText, describeWorld, creatureById, MACHINES, BLOCK, BLOCK_Y0, blockKey, footAt, debrisAt, footing,
-} from './tide-pool-world.js?v=30';
+} from './tide-pool-world.js?v=31';
 
 const root = document.querySelector('[data-tide-pool]');
 const status = document.querySelector('#tide-status');
diff --git a/src/components/tide-pool.tsx b/src/components/tide-pool.tsx
index f615124..94344b8 100644
--- a/src/components/tide-pool.tsx
+++ b/src/components/tide-pool.tsx
@@ -141,7 +141,7 @@ export function TidePoolContent() {
       </details>
       {/* Lets the three.js add-ons resolve the same pinned module the page already uses. */}
       <script type="importmap" dangerouslySetInnerHTML={{ __html: JSON.stringify({ imports: { three: "/public/tide-pool-vendor/three.module.js" } }) }}/>
-      <script type="module" src="/public/tide-pool.js?v=49"></script>
+      <script type="module" src="/public/tide-pool.js?v=50"></script>
     </main>
   );
 }