diff --git a/packages/reactivity/src/baseWatch.ts b/packages/reactivity/src/baseWatch.ts
index 2b1c64dd2..b14c0d28d 100644
--- a/packages/reactivity/src/baseWatch.ts
+++ b/packages/reactivity/src/baseWatch.ts
@@ -123,7 +123,7 @@ export function baseWatch(
     onTrack,
     onTrigger,
   }: BaseWatchOptions = EMPTY_OBJ,
-): ReactiveEffect | undefined {
+): ReactiveEffect {
   const warnInvalidSource = (s: unknown) => {
     onWarn(
       `Invalid watch source: `,
diff --git a/packages/runtime-core/src/apiWatch.ts b/packages/runtime-core/src/apiWatch.ts
index 4a34eec0b..106d9cc78 100644
--- a/packages/runtime-core/src/apiWatch.ts
+++ b/packages/runtime-core/src/apiWatch.ts
@@ -224,17 +224,14 @@ function doWatch(
     handleErrorWithInstance(err, instance, type)
   extendOptions.scheduler = getScheduler(flush)(instance)
 
-  let effect = baseWatch(source, cb, extend({}, options, extendOptions))
-
+  const effect = baseWatch(source, cb, extend({}, options, extendOptions))
   const scope = getCurrentScope()
-  const unwatch = !effect
-    ? NOOP
-    : () => {
-        effect!.stop()
-        if (scope) {
-          remove(scope.effects, effect)
-        }
-      }
+  const unwatch = () => {
+    effect!.stop()
+    if (scope) {
+      remove(scope.effects, effect)
+    }
+  }
 
   if (__SSR__ && ssrCleanup) ssrCleanup.push(unwatch)
   return unwatch
diff --git a/packages/runtime-vapor/src/apiWatch.ts b/packages/runtime-vapor/src/apiWatch.ts
index 2c7cd8f63..9cc0f8e67 100644
--- a/packages/runtime-vapor/src/apiWatch.ts
+++ b/packages/runtime-vapor/src/apiWatch.ts
@@ -7,7 +7,7 @@ import {
   baseWatch,
   getCurrentScope,
 } from '@vue/reactivity'
-import { EMPTY_OBJ, NOOP, extend, isFunction, remove } from '@vue/shared'
+import { EMPTY_OBJ, extend, isFunction, remove } from '@vue/shared'
 import { currentInstance } from './component'
 import {
   type SchedulerFactory,
@@ -159,14 +159,6 @@ function doWatch(
 ): WatchStopHandle {
   const { immediate, deep, flush, once } = options
 
-  // TODO remove in 3.5
-  if (__DEV__ && deep !== void 0 && typeof deep === 'number') {
-    warn(
-      `watch() "deep" option with number value will be used as watch depth in future versions. ` +
-        `Please use a boolean instead to avoid potential breakage.`,
-    )
-  }
-
   if (__DEV__ && !cb) {
     if (immediate !== undefined) {
       warn(
@@ -213,17 +205,14 @@ function doWatch(
     handleErrorWithInstance(err, instance, type)
   extendOptions.scheduler = getScheduler(flush)(instance)
 
-  let effect = baseWatch(source, cb, extend({}, options, extendOptions))
-
+  const effect = baseWatch(source, cb, extend({}, options, extendOptions))
   const scope = getCurrentScope()
-  const unwatch = !effect
-    ? NOOP
-    : () => {
-        effect!.stop()
-        if (scope) {
-          remove(scope.effects, effect)
-        }
-      }
+  const unwatch = () => {
+    effect!.stop()
+    if (scope) {
+      remove(scope.effects, effect)
+    }
+  }
 
   if (__SSR__ && ssrCleanup) ssrCleanup.push(unwatch)
   return unwatch