diff --git a/backend/migrations/075_backfill_trail_activities.sql b/backend/migrations/075_backfill_trail_activities.sql
new file mode 100644
index 00000000..be279399
--- /dev/null
+++ b/backend/migrations/075_backfill_trail_activities.sql
@@ -0,0 +1,34 @@
+-- Migration 075: Backfill and correct trail activities so the activity filter
+-- (e.g. selecting "Biking") only surfaces trails that actually allow that activity.
+--
+-- Three parts, all idempotent (guarded so re-runs are no-ops and so later admin
+-- edits are not clobbered once a row no longer matches the known-bad state):
+--   1. Untagged trails -> 'Hiking' (most are CVNP/Metro foot trails).
+--   2. Drop 'Biking' from 11 footpaths that were mis-tagged as bikeable.
+--   3. Bikeable multi-use trails on the allowlist (Towpath, Bike & Hike, Gateway,
+--      etc.) keep their existing 'Hiking, Biking' tags — no change needed.
+
+BEGIN;
+
+-- 1. Untagged trails -> 'Hiking'
+UPDATE pois
+SET primary_activities = 'Hiking'
+WHERE 'trail' = ANY(poi_roles)
+  AND coalesce(deleted, false) = false
+  AND coalesce(nullif(trim(primary_activities), ''), '') = '';
+
+-- 2. Remove 'Biking' from hiking-only footpaths that were incorrectly tagged.
+-- Element-wise: split on commas, drop the 'Biking' item, rejoin. Guarded by id list
+-- + "still contains Biking" (Postgres word boundaries are \m \M, NOT \b), so it
+-- fires once and re-runs as UPDATE 0. Gateway Trail (West Creek paved connector,
+-- id 1018) and the paved/limestone multi-use trails are intentionally excluded.
+UPDATE pois
+SET primary_activities = (
+      SELECT string_agg(trim(part), ', ')
+      FROM unnest(string_to_array(primary_activities, ',')) AS part
+      WHERE lower(trim(part)) <> 'biking'
+    )
+WHERE id IN (974, 1021, 1036, 1045, 1050, 1057, 1068, 1074, 1089, 1099, 1095)
+  AND primary_activities ~* '\mBiking\M';
+
+COMMIT;
diff --git a/frontend/src/components/Map.jsx b/frontend/src/components/Map.jsx
index 18c18cd9..5eca37e8 100644
--- a/frontend/src/components/Map.jsx
+++ b/frontend/src/components/Map.jsx
@@ -3,7 +3,7 @@ import { createPortal } from 'react-dom';
 import { MapContainer, TileLayer, Marker, Tooltip, useMap, GeoJSON, useMapEvents, CircleMarker } from 'react-leaflet';
 import L from 'leaflet';
 import VirtualPoiCreator from './VirtualPoiCreator';
-import { getDestinationIconTypeFromConfig, poiMatchesActivityForTypes, matchesWholeWord } from '../utils/iconUtils';
+import { getDestinationIconTypeFromConfig, poiMatchesActivityForTypes, trailPassesActivityFilter, matchesWholeWord } from '../utils/iconUtils';
 import { useTrip } from '../hooks/useTrip';
 import { useNavigate } from 'react-router-dom';
 import { generateSlug } from './sidebar/helpers';
@@ -635,7 +635,7 @@ function MapBoundsTracker({ destinations, visibleTypes, getDestinationIconType,
             // Title search matches across all linear types, ignoring layer toggles
             isLayerVisible = feature.name?.toLowerCase().includes(search);
           } else if (feature.poi_roles?.includes('trail')) {
-            isLayerVisible = showTrails;
+            isLayerVisible = showTrails && trailPassesActivityFilter(feature, visibleTypes, iconConfig);
           } else if (feature.poi_roles?.includes('river')) {
             isLayerVisible = showRivers;
           } else if (feature.poi_roles?.includes('water_taxi')) {
@@ -1495,7 +1495,7 @@ function Map({ destinations, selectedPoi, selectedIsLinear, onSelectPoi, isAdmin
           // regardless of its layer toggle, and hide non-matches.
           const isVisible = searchQuery
             ? feature.name?.toLowerCase().includes(searchQuery.toLowerCase())
-            : ((feature.poi_roles?.includes('trail') && showTrails) ||
+            : ((feature.poi_roles?.includes('trail') && showTrails && trailPassesActivityFilter(feature, visibleTypes, iconConfig)) ||
                (feature.poi_roles?.includes('river') && showRivers) ||
                (feature.poi_roles?.includes('water_taxi') && showWaterTaxis) ||
                (feature.poi_roles?.includes('boundary') && visibleBoundaries.has(feature.id)));
diff --git a/frontend/src/utils/iconUtils.js b/frontend/src/utils/iconUtils.js
index 3a423f54..cbf2801d 100644
--- a/frontend/src/utils/iconUtils.js
+++ b/frontend/src/utils/iconUtils.js
@@ -61,6 +61,34 @@ export function poiMatchesActivityForTypes(poi, visibleTypes, iconConfig) {
   return false;
 }
 
+/**
+ * True when the legend is narrowed to a subset of activity-bearing types
+ * (e.g. just "Biking") rather than showing everything. The Trails layer is only
+ * refined by activity while this is true; with all (or no) activity types
+ * selected it stays all-or-nothing, preserving plain "show me the trails" browsing.
+ */
+export function isActivityFilterActive(visibleTypes, iconConfig) {
+  if (!iconConfig || iconConfig.length === 0) return false;
+  let activityTypes = 0, selected = 0;
+  for (const icon of iconConfig) {
+    if (icon.enabled === false || !icon.activity_fallbacks) continue;
+    activityTypes++;
+    if (visibleTypes.has(icon.name)) selected++;
+  }
+  return selected > 0 && selected < activityTypes;
+}
+
+/**
+ * Whether a trail (linear feature) should render given the current activity
+ * narrowing. Untagged trails always show, so a missing tag never silently hides a
+ * trail. (Selecting "Biking" hides hiking-only trails.)
+ */
+export function trailPassesActivityFilter(feature, visibleTypes, iconConfig) {
+  if (!isActivityFilterActive(visibleTypes, iconConfig)) return true;
+  if (!(feature.primary_activities || '').trim()) return true;
+  return poiMatchesActivityForTypes(feature, visibleTypes, iconConfig);
+}
+
 export function getIconUrlForPOI(poi, iconConfig, poiType) {
   if (poiType === 'trail') return '/icons/layers/trails.svg';
   if (poiType === 'river') return '/icons/layers/rivers.svg';