diff --git a/src/mikeio/dfs/_dfs1.py b/src/mikeio/dfs/_dfs1.py
index 9756f2972..f37cc126d 100644
--- a/src/mikeio/dfs/_dfs1.py
+++ b/src/mikeio/dfs/_dfs1.py
@@ -87,11 +87,12 @@ class Dfs1(_Dfs123):
     def __init__(self, filename: str | Path) -> None:
         super().__init__(filename)
 
-        self._dfs = DfsFileFactory.Dfs1FileOpen(str(filename))
-        self._x0: float = self._dfs.SpatialAxis.X0
-        self._dx: float = self._dfs.SpatialAxis.Dx
-        self._nx: int = self._dfs.SpatialAxis.XCount
-        self._title: str = self._dfs.FileInfo.FileTitle
+        dfs = DfsFileFactory.Dfs1FileOpen(str(filename))
+        self._x0: float = dfs.SpatialAxis.X0
+        self._dx: float = dfs.SpatialAxis.Dx
+        self._nx: int = dfs.SpatialAxis.XCount
+        self._title: str = dfs.FileInfo.FileTitle
+        dfs.Close()
 
         origin = self._longitude, self._latitude
         self._geometry = Grid1D(
diff --git a/src/mikeio/dfs/_dfs3.py b/src/mikeio/dfs/_dfs3.py
index b7e1489f0..5a8633f13 100644
--- a/src/mikeio/dfs/_dfs3.py
+++ b/src/mikeio/dfs/_dfs3.py
@@ -138,22 +138,21 @@ def __init__(self, filename: str | Path):
         )
 
     def _read_dfs3_header(self, read_x0y0z0: bool = False) -> None:
-        self._dfs = DfsFileFactory.Dfs3FileOpen(self._filename)
-
-        self._source = self._dfs
+        dfs = DfsFileFactory.Dfs3FileOpen(self._filename)
 
         if read_x0y0z0:
-            self._x0 = self._dfs.SpatialAxis.X0
-            self._y0 = self._dfs.SpatialAxis.Y0
-            self._z0 = self._dfs.SpatialAxis.Z0
-
-        self._dx = self._dfs.SpatialAxis.Dx
-        self._dy = self._dfs.SpatialAxis.Dy
-        self._dz = self._dfs.SpatialAxis.Dz
-        self._nx = self._dfs.SpatialAxis.XCount
-        self._ny = self._dfs.SpatialAxis.YCount
-        self._nz = self._dfs.SpatialAxis.ZCount
-        self._title = self._dfs.FileInfo.FileTitle
+            self._x0 = dfs.SpatialAxis.X0
+            self._y0 = dfs.SpatialAxis.Y0
+            self._z0 = dfs.SpatialAxis.Z0
+
+        self._dx = dfs.SpatialAxis.Dx
+        self._dy = dfs.SpatialAxis.Dy
+        self._dz = dfs.SpatialAxis.Dz
+        self._nx = dfs.SpatialAxis.XCount
+        self._ny = dfs.SpatialAxis.YCount
+        self._nz = dfs.SpatialAxis.ZCount
+        self._title = dfs.FileInfo.FileTitle
+        dfs.Close()
 
     def read(
         self,
diff --git a/src/mikeio/dfsu/_dfsu.py b/src/mikeio/dfsu/_dfsu.py
index 73915f691..61cc105ea 100644
--- a/src/mikeio/dfsu/_dfsu.py
+++ b/src/mikeio/dfsu/_dfsu.py
@@ -580,6 +580,7 @@ def _dfs_read_item_time_func(
     ) -> tuple[np.ndarray, pd.Timestamp]:
         dfs = DfsuFile.Open(self._filename)
         itemdata = dfs.ReadItemTimeStep(item + 1, step)
+        dfs.Close()
 
         return itemdata.Data, itemdata.Time
 
diff --git a/src/mikeio/generic.py b/src/mikeio/generic.py
index d2b73b06c..98439b7ec 100644
--- a/src/mikeio/generic.py
+++ b/src/mikeio/generic.py
@@ -819,6 +819,8 @@ def avg_time(
             outdatalist[item][has_value] += d[has_value]
             steps_list[item][has_value] += 1
 
+    dfs_i.Close()
+
     for item in range(n_items):
         darray = np.zeros_like(outdatalist[item], dtype=np.float32)
         if skipna:
@@ -945,6 +947,8 @@ def quantile(
         # TODO should this be static Z coordinates instead?
         dfs_o.WriteItemTimeStepNext(0.0, znitemdata.Data)
 
+    dfs_i.Close()
+
     for item in range(n_items_out):
         darray = outdatalist[item].astype(np.float32)
         dfs_o.WriteItemTimeStepNext(0.0, darray)
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 000000000..a4fd656bc
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,27 @@
+"""Shared test fixtures and utilities."""
+
+import os
+import platform
+from pathlib import Path
+
+
+def _count_fds_for_file(filename: str) -> int:
+    """Count open file descriptors pointing to a specific filename on Linux.
+
+    Uses /proc/self/fd readlinks to identify descriptors matching the target file.
+    Returns 0 on non-Linux platforms.
+    """
+    if platform.system() != "Linux":
+        return 0
+
+    target = str(Path(filename).resolve())
+    count = 0
+    fd_dir = "/proc/self/fd"
+    for entry in os.listdir(fd_dir):
+        try:
+            link = os.readlink(os.path.join(fd_dir, entry))
+            if link == target:
+                count += 1
+        except OSError:
+            continue
+    return count
diff --git a/tests/test_dfs1.py b/tests/test_dfs1.py
index c1db72338..3eff1d863 100644
--- a/tests/test_dfs1.py
+++ b/tests/test_dfs1.py
@@ -1,9 +1,12 @@
 from pathlib import Path
+import platform
+
 import numpy as np
 import pytest
 import pandas as pd
 
 import mikeio
+from mikecore.DfsFileFactory import DfsFileFactory
 
 
 def test_filenotexist() -> None:
@@ -204,3 +207,43 @@ def test_interp_onepoint_dfs1() -> None:
 
     with pytest.raises(AssertionError, match="not possible for Grid1D with one point"):
         ds[0].interp(x=0)
+
+
+@pytest.mark.skipif(
+    platform.system() != "Linux",
+    reason="File descriptor counting via /proc only works on Linux",
+)
+def test_count_open_fds_sanity_check() -> None:
+    """Verify _count_fds_for_file detects mikecore file handles."""
+    from conftest import _count_fds_for_file
+
+    filename = "tests/testdata/random.dfs1"
+    assert _count_fds_for_file(filename) == 0
+
+    dfs = DfsFileFactory.DfsGenericOpen(filename)
+    try:
+        assert _count_fds_for_file(filename) >= 1, "opening a file must increase FD count"
+    finally:
+        dfs.Close()
+
+    assert _count_fds_for_file(filename) == 0, "closing a file must restore FD count"
+
+
+@pytest.mark.skipif(
+    platform.system() != "Linux",
+    reason="File descriptor counting via /proc only works on Linux",
+)
+def test_dfs1_init_closes_file_handle() -> None:
+    """Dfs1.__init__ must not leak a file handle.
+
+    Before the fix, Dfs1.__init__ stored the open handle in self._dfs
+    without closing it, so each live instance held one file descriptor.
+    """
+    from conftest import _count_fds_for_file
+
+    filename = "tests/testdata/random.dfs1"
+    instances = []
+    for _ in range(50):
+        instances.append(mikeio.Dfs1(filename))
+
+    assert _count_fds_for_file(filename) == 0
diff --git a/tests/test_dfs2.py b/tests/test_dfs2.py
index 2aa3989e4..526a44c75 100644
--- a/tests/test_dfs2.py
+++ b/tests/test_dfs2.py
@@ -1,5 +1,7 @@
 from pathlib import Path
 import datetime
+import platform
+from typing import Any
 from matplotlib import pyplot as plt
 import numpy as np
 import pandas as pd
@@ -939,3 +941,44 @@ def test_append_mismatch_geometry(tmp_path: Path) -> None:
     dfs = mikeio.Dfs2(new_filename)
     with pytest.raises(ValueError, match="geometry"):
         dfs.append(ds2)
+
+
+@pytest.mark.skipif(
+    platform.system() != "Linux",
+    reason="File descriptor counting via /proc only works on Linux",
+)
+def test_dfs2_init_closes_file_handle() -> None:
+    """Dfs2.__init__ must not leak a file handle.
+
+    Dfs2.__init__ opens a Dfs2FileOpen handle to read spatial axis info
+    and must close it before returning.
+    """
+    from conftest import _count_fds_for_file
+
+    filename = "tests/testdata/eq.dfs2"
+    instances = []
+    for _ in range(50):
+        instances.append(mikeio.Dfs2(filename))
+
+    assert _count_fds_for_file(filename) == 0
+
+
+@pytest.mark.skipif(
+    platform.system() != "Linux",
+    reason="File descriptor counting via /proc only works on Linux",
+)
+def test_dfs2_read_closes_file_handle() -> None:
+    """Dfs2.read() must not leak file handles.
+
+    Each read() opens a Dfs2FileOpen handle via _open();
+    it must be closed before returning.
+    """
+    from conftest import _count_fds_for_file
+
+    filename = "tests/testdata/eq.dfs2"
+    results = []
+    for _ in range(50):
+        dfs = mikeio.Dfs2(filename)
+        results.append(dfs.read())
+
+    assert _count_fds_for_file(filename) == 0
diff --git a/tests/test_dfs3.py b/tests/test_dfs3.py
index 86065b4f2..d0ed2fae8 100644
--- a/tests/test_dfs3.py
+++ b/tests/test_dfs3.py
@@ -1,4 +1,6 @@
 from pathlib import Path
+import platform
+
 import pytest
 import numpy as np
 
@@ -287,6 +289,26 @@ def test_append_dfs3(tmp_path: Path) -> None:
     dfs.append(ds2)
 
 
+@pytest.mark.skipif(
+    platform.system() != "Linux",
+    reason="File descriptor counting via /proc only works on Linux",
+)
+def test_dfs3_init_closes_file_handle() -> None:
+    """Dfs3._read_dfs3_header must not leak a file handle.
+
+    Before the fix, _read_dfs3_header stored the open handle in
+    self._dfs without closing it.
+    """
+    from conftest import _count_fds_for_file
+
+    filename = "tests/testdata/Grid1.dfs3"
+    instances = []
+    for _ in range(50):
+        instances.append(mikeio.Dfs3(filename))
+
+    assert _count_fds_for_file(filename) == 0
+
+
 def test_read_with_title() -> None:
     sourcefilename = "tests/testdata/single_layer.dfs3"
     dfs = mikeio.Dfs3(sourcefilename)
diff --git a/tests/test_dfsu2dh.py b/tests/test_dfsu2dh.py
index 1df5649ad..d65db727d 100644
--- a/tests/test_dfsu2dh.py
+++ b/tests/test_dfsu2dh.py
@@ -1,3 +1,4 @@
+import platform
 import shutil
 from pathlib import Path
 
@@ -1037,6 +1038,26 @@ def test_dfsu_to_xarray_has_element_coordinates() -> None:
     assert xr_da.z.values[example_quad_element] == approx(example_quad_coordinates[2])
 
 
+@pytest.mark.skipif(
+    platform.system() != "Linux",
+    reason="File descriptor counting via /proc only works on Linux",
+)
+def test_dfsu_read_closes_file_handle() -> None:
+    """Dfsu read must not leak file handles.
+
+    Each read() opens a DfsuFile; it must be closed before returning.
+    """
+    from conftest import _count_fds_for_file
+
+    filename = "tests/testdata/HD2D.dfsu"
+    results = []
+    for _ in range(50):
+        dfs = mikeio.open(filename)
+        results.append(dfs.read())
+
+    assert _count_fds_for_file(filename) == 0
+
+
 def test_write_dfsu_with_title(tmp_path: Path) -> None:
     """Test writing a dfsu file with a custom title and reading it back."""
     sourcefilename = "tests/testdata/HD2D.dfsu"