diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Changelog
 
+## 0.2.1 - 2022-10-24:
+
+* fix: Fix excessive memory use when using why-depends on large dependency graphs (issue: [@31][])
+
+[#25]: https://github.com/utdemir/nix-tree/issues/31
+
 ## 0.2.0 - 2022-01-02:
 
 * feat: Support passing flake references (issue: [#27][])
diff --git a/nix-tree.cabal b/nix-tree.cabal
--- a/nix-tree.cabal
+++ b/nix-tree.cabal
@@ -3,7 +3,7 @@
 name:                nix-tree
 synopsis:            Interactively browse a Nix store paths dependencies
 description:         A terminal curses application to browse a Nix store paths dependencies
-version:             0.2.0
+version:             0.2.1
 homepage:            https://github.com/utdemir/nix-tree
 license:             BSD-3-Clause
 license-file:        LICENSE
diff --git a/src/NixTree/App.hs b/src/NixTree/App.hs
--- a/src/NixTree/App.hs
+++ b/src/NixTree/App.hs
@@ -195,7 +195,7 @@
           -- main screen
           (B.VtyEvent (V.EvKey k []), Nothing)
             | k `elem` [V.KChar 'q', V.KEsc] ->
-              B.halt s
+                B.halt s
           (B.VtyEvent (V.EvKey (V.KChar '?') []), Nothing) ->
             B.continue s {aeOpenModal = Just (ModalNotice helpNotice)}
           (B.VtyEvent (V.EvKey (V.KChar 'w') []), Nothing) -> do
@@ -217,16 +217,16 @@
                 & sortPanes
           (B.VtyEvent (V.EvKey k []), Nothing)
             | k `elem` [V.KChar 'h', V.KLeft] ->
-              B.continue $ moveLeft s
+                B.continue $ moveLeft s
           (B.VtyEvent (V.EvKey k []), Nothing)
             | k `elem` [V.KChar 'j', V.KDown, V.KChar '\t'] ->
-              B.continue $ move B.listMoveDown s
+                B.continue $ move B.listMoveDown s
           (B.VtyEvent (V.EvKey k []), Nothing)
             | k `elem` [V.KChar 'k', V.KUp, V.KBackTab] ->
-              B.continue $ move B.listMoveUp s
+                B.continue $ move B.listMoveUp s
           (B.VtyEvent (V.EvKey k []), Nothing)
             | k `elem` [V.KChar 'l', V.KRight] ->
-              B.continue $ moveRight s
+                B.continue $ moveRight s
           (B.VtyEvent (V.EvKey V.KPageUp []), Nothing) ->
             B.continue =<< moveF B.listMovePageUp s
           (B.VtyEvent (V.EvKey V.KPageDown []), Nothing) ->
@@ -234,21 +234,21 @@
           -- why-depends modal
           (B.VtyEvent (V.EvKey k []), Just (ModalWhyDepends _))
             | k `elem` [V.KChar 'q', V.KEsc] ->
-              B.continue s {aeOpenModal = Nothing}
+                B.continue s {aeOpenModal = Nothing}
           (B.VtyEvent (V.EvKey k []), Just (ModalWhyDepends _))
             | k `elem` [V.KChar 'h', V.KLeft] -> do
-              B.hScrollBy (B.viewportScroll WidgetWhyDependsViewport) (-1)
-              B.continue s
+                B.hScrollBy (B.viewportScroll WidgetWhyDependsViewport) (-1)
+                B.continue s
           (B.VtyEvent (V.EvKey k []), Just (ModalWhyDepends l))
             | k `elem` [V.KChar 'j', V.KDown, V.KChar '\t'] ->
-              B.continue s {aeOpenModal = Just $ ModalWhyDepends (B.listMoveDown l)}
+                B.continue s {aeOpenModal = Just $ ModalWhyDepends (B.listMoveDown l)}
           (B.VtyEvent (V.EvKey k []), Just (ModalWhyDepends l))
             | k `elem` [V.KChar 'k', V.KUp, V.KBackTab] ->
-              B.continue s {aeOpenModal = Just $ ModalWhyDepends (B.listMoveUp l)}
+                B.continue s {aeOpenModal = Just $ ModalWhyDepends (B.listMoveUp l)}
           (B.VtyEvent (V.EvKey k []), Just (ModalWhyDepends _))
             | k `elem` [V.KChar 'l', V.KRight] -> do
-              B.hScrollBy (B.viewportScroll WidgetWhyDependsViewport) 1
-              B.continue s
+                B.hScrollBy (B.viewportScroll WidgetWhyDependsViewport) 1
+                B.continue s
           (B.VtyEvent (V.EvKey V.KPageUp []), Just (ModalWhyDepends l)) ->
             B.listMovePageUp l >>= \l' ->
               B.continue s {aeOpenModal = Just $ ModalWhyDepends l'}
@@ -265,10 +265,10 @@
             B.continue s {aeOpenModal = Nothing}
           (B.VtyEvent (V.EvKey k []), Just (ModalSearch l r xs))
             | k `elem` [V.KDown, V.KChar '\t'] ->
-              B.continue s {aeOpenModal = Just $ ModalSearch l r (B.listMoveDown xs)}
+                B.continue s {aeOpenModal = Just $ ModalSearch l r (B.listMoveDown xs)}
           (B.VtyEvent (V.EvKey k []), Just (ModalSearch l r xs))
             | k `elem` [V.KUp, V.KBackTab] ->
-              B.continue s {aeOpenModal = Just $ ModalSearch l r (B.listMoveUp xs)}
+                B.continue s {aeOpenModal = Just $ ModalSearch l r (B.listMoveUp xs)}
           (B.VtyEvent (V.EvKey V.KLeft []), Just (ModalSearch l r xs)) ->
             B.continue
               s
@@ -283,7 +283,7 @@
                 }
           (B.VtyEvent (V.EvKey (V.KChar c) []), Just (ModalSearch l r _))
             | c `Set.member` allowedSearchChars ->
-              B.continue (showAndUpdateSearch (l <> T.singleton c) r s)
+                B.continue (showAndUpdateSearch (l <> T.singleton c) r s)
           (B.VtyEvent (V.EvKey (V.KBS) []), Just (ModalSearch l r _)) ->
             B.continue (showAndUpdateSearch (T.dropEnd 1 l) r s)
           (B.VtyEvent (V.EvKey V.KEnter []), Just (ModalSearch _ _ xs)) ->
@@ -298,7 +298,7 @@
           -- notices
           (B.VtyEvent (V.EvKey k []), Just (ModalNotice _))
             | k `elem` [V.KChar 'q', V.KEsc] ->
-              B.continue s {aeOpenModal = Nothing}
+                B.continue s {aeOpenModal = Nothing}
           -- handle our events
           (B.AppEvent (EventTick t), _) ->
             let new = s {aeCurrTime = t}
@@ -339,8 +339,8 @@
           Notice
             "Error"
             ( T.intercalate "\n" $
-                "Cannot copy to clipboard: " :
-                map ("  " <>) errs
+                "Cannot copy to clipboard: "
+                  : map ("  " <>) errs
                   ++ ["Please report this as a bug."]
             )
 
@@ -383,7 +383,9 @@
             if null immediateParents
               then "Immediate Parents: -"
               else
-                "Immediate Parents (" <> T.pack (show $ length immediateParents) <> "): "
+                "Immediate Parents ("
+                  <> T.pack (show $ length immediateParents)
+                  <> "): "
                   <> T.intercalate ", " (map storeNameToShortText immediateParents)
         ]
   where
@@ -455,9 +457,11 @@
   renderModal "Search" window
   where
     window =
-      B.txt left B.<+> B.txt "|" B.<+> B.txt right
-        B.<=> B.hBorder
-        B.<=> renderList Nothing True l
+      B.txt left
+        B.<+> B.txt "|"
+        B.<+> B.txt right
+          B.<=> B.hBorder
+          B.<=> renderList Nothing True l
 
 showAndUpdateSearch :: Text -> Text -> AppEnv s -> AppEnv s
 showAndUpdateSearch left right env@AppEnv {aeInvertedIndex} =
@@ -491,12 +495,12 @@
 moveRight env@AppEnv {aePrevPane, aeCurrPane, aeNextPane, aeParents}
   | null (B.listElements aeNextPane) = env
   | otherwise =
-    env
-      { aePrevPane = aeCurrPane {B.listName = WidgetPrevPane},
-        aeCurrPane = aeNextPane {B.listName = WidgetCurrPane},
-        aeParents = aePrevPane : aeParents
-      }
-      & repopulateNextPane
+      env
+        { aePrevPane = aeCurrPane {B.listName = WidgetPrevPane},
+          aeCurrPane = aeNextPane {B.listName = WidgetCurrPane},
+          aeParents = aePrevPane : aeParents
+        }
+        & repopulateNextPane
 
 repopulateNextPane :: AppEnv s -> AppEnv s
 repopulateNextPane env@AppEnv {aeActualStoreEnv, aeNextPane, aeSortOrder} =
@@ -547,7 +551,7 @@
 selectPath :: NonEmpty (Path s) -> AppEnv s -> AppEnv s
 selectPath path env
   | (spName <$> path) == (spName <$> selectedPaths env) =
-    env
+      env
 selectPath path env@AppEnv {aeActualStoreEnv} =
   let root :| children = NE.reverse path
       lists =
diff --git a/src/NixTree/PathStats.hs b/src/NixTree/PathStats.hs
--- a/src/NixTree/PathStats.hs
+++ b/src/NixTree/PathStats.hs
@@ -37,8 +37,8 @@
                 [ (spName, const () <$> sp)
                   | sp@StorePath {spName} <- spRefs curr,
                     env spName
-                ] :
-              map (ipsAllRefs . spPayload) (spRefs curr)
+                ]
+                : map (ipsAllRefs . spPayload) (spRefs curr)
             )
       }
 
@@ -92,24 +92,6 @@
 calculatePathStats :: StoreEnv s () -> StoreEnv s (PathStats s)
 calculatePathStats = mkFinalEnv . mkIntermediateEnv (const True)
 
-whyDepends :: StoreEnv s a -> StoreName s -> [NonEmpty (StorePath s (StoreName s) a)]
-whyDepends env name =
-  seBottomUp
-    ( \curr ->
-        if spName curr == name
-          then [curr {spRefs = map spName (spRefs curr)} :| []]
-          else
-            concat . transpose $
-              map
-                (map (curr {spRefs = map spName (spRefs curr)} NE.<|) . spPayload)
-                (spRefs curr)
-    )
-    env
-    & seGetRoots
-    & fmap spPayload
-    & concat
-    & map NE.reverse
-
 -- TODO: This can be precomputed.
 shortestPathTo :: StoreEnv s a -> StoreName s -> NonEmpty (StorePath s (StoreName s) a)
 shortestPathTo env name =
@@ -135,3 +117,57 @@
     & minimumBy (comparing fst)
     & snd
     & NE.reverse
+
+-- Why depends implementation
+
+-- We iterate the dependency graph bottom up. Every node contains a set of paths which represent
+-- the why-depends output from that node down. The set of paths is represented as a "Treeish" object,
+-- which is a trie-like structure.
+whyDepends :: forall s a. StoreEnv s a -> StoreName s -> [NonEmpty (StorePath s (StoreName s) a)]
+whyDepends env name =
+  seBottomUp @_ @_ @(Maybe (Treeish (StorePath s (StoreName s) a)))
+    ( \curr ->
+        if spName curr == name
+          then Just $ mkTreeish (curr {spRefs = map spName (spRefs curr)}) []
+          else
+            spRefs curr
+              & map spPayload
+              & catMaybes
+              & NE.nonEmpty
+              <&> NE.toList
+              <&> mkTreeish (curr {spRefs = map spName (spRefs curr)})
+              <&> capTreeish 1_000_000
+    )
+    env
+    & seGetRoots
+    & fmap spPayload
+    & NE.toList
+    & catMaybes
+    & take 10000
+    & concatMap treeishToList
+
+-- A trie-like structure which also caches the size.
+data Treeish a = Treeish Int a [Treeish a]
+
+mkTreeish :: a -> [Treeish a] -> Treeish a
+mkTreeish a ts = Treeish (1 + sum (map (\(Treeish i _ _) -> i) ts)) a ts
+
+treeishSize :: Treeish a -> Int
+treeishSize (Treeish i _ _) = i
+
+capTreeish :: Int -> Treeish a -> Treeish a
+capTreeish cap (Treeish i a ts)
+  | i <= cap = Treeish i a ts
+  | otherwise = Treeish cap a (go cap ts)
+  where
+    go _ [] = []
+    go remaining (x : xs) =
+      let x' = capTreeish remaining x
+          remaining' = remaining - treeishSize x'
+       in if remaining > 0
+            then x' : go remaining' xs
+            else [x']
+
+treeishToList :: Treeish a -> [NonEmpty a]
+treeishToList (Treeish _ a []) = [a :| []]
+treeishToList (Treeish _ a xs) = map (a NE.<|) (concatMap treeishToList xs)
diff --git a/src/NixTree/StorePath.hs b/src/NixTree/StorePath.hs
--- a/src/NixTree/StorePath.hs
+++ b/src/NixTree/StorePath.hs
@@ -203,7 +203,8 @@
   nixVersion <- liftIO getNixVersion
 
   when (isDerivation && nixVersion < Nix2_4) $
-    liftIO $ hPutStrLn stderr "Warning: --derivation flag is ignored on Nix versions older than 2.4."
+    liftIO $
+      hPutStrLn stderr "Warning: --derivation flag is ignored on Nix versions older than 2.4."
 
   roots <-
     liftIO $
@@ -261,11 +262,11 @@
       | HS.member name visited = (acc, visited)
       | not (predicate name) = (acc, visited)
       | otherwise =
-        let sp@StorePath {spRefs} = seLookup env name
-         in foldl'
-              (\(acc', visited') name' -> go acc' visited' name')
-              (sp : acc, HS.insert name visited)
-              spRefs
+          let sp@StorePath {spRefs} = seLookup env name
+           in foldl'
+                (\(acc', visited') name' -> go acc' visited' name')
+                (sp : acc, HS.insert name visited)
+                spRefs
 
 seBottomUp ::
   forall s a b.