diff --git a/environment.yml b/environment.yml
index 8ec65dc..408533b 100644
--- a/environment.yml
+++ b/environment.yml
@@ -14,3 +14,4 @@ dependencies:
   - numpy
   - shapely
   - pyarrow
+  - fiona
diff --git a/pyproject.toml b/pyproject.toml
index aae1889..42acc35 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -9,7 +9,7 @@ description = "Conveniently search, download, and preprocess ArcticDEM and REMA
 keywords = [ "geospatial", "elevation", "arcticdem", "rema", "dem",]
 classifiers = [ "Intended Audience :: Science/Research", "Programming Language :: Python :: 3", "License :: OSI Approved :: MIT License", "Operating System :: OS Independent", "Topic :: Scientific/Engineering", "Topic :: Scientific/Engineering :: GIS", "Topic :: Scientific/Engineering :: Image Processing",]
 requires-python = ">=3.9"
-dependencies = ["rioxarray", "rasterio", "geopandas", "pandas", "shapely", "numpy", "GDAL", "opencv-python", "scipy", "numba", "pyarrow",]  # GDAL
+dependencies = ["rioxarray", "rasterio", "geopandas", "pandas", "shapely", "numpy", "GDAL", "opencv-python", "scipy", "numba", "pyarrow", "fiona"]  # GDAL
 
 [[project.authors]]
 name = "Tom Chudley"
diff --git a/src/pdemtools/load.py b/src/pdemtools/load.py
index 85071e2..e1ca46a 100644
--- a/src/pdemtools/load.py
+++ b/src/pdemtools/load.py
@@ -313,20 +313,22 @@ def mosaic(
         )
 
     # Load tiles that intersect with AOI
-    tiles = gpd.read_file(
-        _get_index_fpath(dataset, version=version), layer=layer, bbox=bounds
-    )
+    index_fpath =  _get_index_fpath(dataset, version=version)
+    with open(index_fpath, "rb") as file:
+        tiles = gpd.read_file(index_fpath, layer=layer, bbox=bounds, engine='fiona') 
 
-    if len(tiles) < 1:
-        raise ValueError(
-            "No {dataset} mosaic tiles found to intersect with bounds {aoi}"
-        )
+        if len(tiles) < 1:
+            raise ValueError(
+                "No {dataset} mosaic tiles found to intersect with bounds {aoi}"
+            )
+
+        # get aws filepaths from the tiles dataframe
+        fpaths = []
+        for _, row in tiles.iterrows():
+            fpath = _aws_link(row, dataset=dataset, version=version, resolution=resolution)
+            fpaths.append(fpath)
 
-    # get aws filepaths from the tiles dataframe
-    fpaths = []
-    for _, row in tiles.iterrows():
-        fpath = _aws_link(row, dataset=dataset, version=version, resolution=resolution)
-        fpaths.append(fpath)
+        tiles = None  # release tiles object
 
     # remove duplicates in 10m and 32m (which load supertiles, not tiles)
     fpaths = list(set(fpaths))
@@ -349,6 +351,7 @@ def mosaic(
     # Filter -9999.0 values to np.nan
     dem = dem.where(dem > -9999.0)
 
+    dems = None  # release dem objects for memory management
     return dem