diff --git a/dataretrieval/waterdata/utils.py b/dataretrieval/waterdata/utils.py
index dd622efd..ad1b3afd 100644
--- a/dataretrieval/waterdata/utils.py
+++ b/dataretrieval/waterdata/utils.py
@@ -2024,9 +2024,18 @@ def _get_args(
             args[k] = _as_str_list(v, k)
         elif (
             k in _NO_NORMALIZE_PARAMS
-            or isinstance(v, str)
-            or not isinstance(v, Iterable)
+            and isinstance(v, Iterable)
+            and not isinstance(v, str)
         ):
+            # Numeric params (water_year, bbox, thresholds, …) keep their
+            # element types — no string-normalization — but a non-string
+            # iterable (numpy array, pandas Series, generator) is materialized
+            # to a list so the GET comma-join and the chunker, which test
+            # ``list``/``tuple``, handle it instead of str()-ing the whole
+            # array. ``.tolist()`` yields native int/float; ``list()`` covers
+            # generators and other iterables. Scalars/strings fall through.
+            args[k] = v.tolist() if hasattr(v, "tolist") else list(v)
+        elif isinstance(v, str) or not isinstance(v, Iterable):
             args[k] = v
         else:
             args[k] = _normalize_str_iterable(v, k)
diff --git a/tests/waterdata_test.py b/tests/waterdata_test.py
index 47bc4458..3358899b 100644
--- a/tests/waterdata_test.py
+++ b/tests/waterdata_test.py
@@ -35,6 +35,7 @@
     _check_profiles,
     _construct_api_requests,
     _construct_cql_request,
+    _get_args,
     _normalize_str_iterable,
 )
 
@@ -294,6 +295,27 @@ def test_construct_api_requests_numeric_list_joins_with_str():
     assert "water_year=2020%2C2021" in str(req.url)
 
 
+def test_get_args_materializes_numpy_and_series_numeric_params():
+    """Regression: numeric (_NO_NORMALIZE_PARAMS) params given as a numpy array
+    or pandas Series must be materialized to a list of native Python scalars so
+    they comma-join in the URL (and stay JSON-serializable) — previously the
+    array/Series repr leaked into the query string."""
+    for value in (np.array([2020, 2021]), pd.Series([2020, 2021])):
+        args = _get_args({"water_year": value})
+        assert args["water_year"] == [2020, 2021]
+        # native Python ints, not numpy scalars (JSON-serializable, no np reprs)
+        assert [type(x) for x in args["water_year"]] == [int, int]
+        req = _construct_api_requests("peaks", **args)
+        assert "water_year=2020%2C2021" in str(req.url)
+
+    # float coordinate arrays (e.g. bbox) likewise materialize to native floats
+    args = _get_args({"bbox": np.array([-92.8, 44.2, -88.9, 46.0])})
+    assert args["bbox"] == [-92.8, 44.2, -88.9, 46.0]
+    assert all(type(x) is float for x in args["bbox"])
+    req = _construct_api_requests("daily", **args)
+    assert "bbox=-92.8%2C44.2%2C-88.9%2C46.0" in str(req.url)
+
+
 def test_construct_api_requests_two_element_date_list_becomes_interval():
     """A two-element date list is interpreted as start/end of an OGC datetime
     interval (joined with '/'), NOT as two discrete dates. The OGC `datetime`