diff --git a/google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1/StreamWriter.java b/google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1/StreamWriter.java
index c9c27fae9e..4d07dfdd91 100644
--- a/google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1/StreamWriter.java
+++ b/google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1/StreamWriter.java
@@ -47,7 +47,10 @@ public class StreamWriter implements AutoCloseable {
   private static final Logger log = Logger.getLogger(StreamWriter.class.getName());
 
   private static String datasetsMatching = "projects/[^/]+/datasets/[^/]+/";
-  private static Pattern streamPattern = Pattern.compile(datasetsMatching);
+  private static Pattern streamPatternDatasets = Pattern.compile(datasetsMatching);
+
+  private static String defaultStreamMatching = "/_default";
+  private static Pattern streamPatternDefaultStream = Pattern.compile(defaultStreamMatching);
 
   // Cache of location info for a given dataset.
   private static Map<String, String> projectAndDatasetToLocation = new ConcurrentHashMap<>();
@@ -195,6 +198,14 @@ private StreamWriter(Builder builder) throws IOException {
                   getBigQueryWriteClient(builder),
                   ownsBigQueryWriteClient));
     } else {
+      if (!isDefaultStream(streamName)) {
+        log.warning(
+            "Connection pool is only allowed in default stream! However received "
+                + builder.streamName);
+        throw new IllegalArgumentException(
+            "Trying to enable connection pool in non-default stream.");
+      }
+
       BigQueryWriteClient client = getBigQueryWriteClient(builder);
       String location = builder.location;
       if (location == null || location.isEmpty()) {
@@ -264,7 +275,7 @@ private StreamWriter(Builder builder) throws IOException {
 
   @VisibleForTesting
   static String extractDatasetAndProjectName(String streamName) {
-    Matcher streamMatcher = streamPattern.matcher(streamName);
+    Matcher streamMatcher = streamPatternDatasets.matcher(streamName);
     if (streamMatcher.find()) {
       return streamMatcher.group();
     } else {
@@ -273,6 +284,12 @@ static String extractDatasetAndProjectName(String streamName) {
     }
   }
 
+  @VisibleForTesting
+  static boolean isDefaultStream(String streamName) {
+    Matcher streamMatcher = streamPatternDefaultStream.matcher(streamName);
+    return streamMatcher.find();
+  }
+
   private BigQueryWriteClient getBigQueryWriteClient(Builder builder) throws IOException {
     if (builder.client == null) {
       BigQueryWriteSettings stubSettings =
diff --git a/google-cloud-bigquerystorage/src/test/java/com/google/cloud/bigquery/storage/v1/JsonStreamWriterTest.java b/google-cloud-bigquerystorage/src/test/java/com/google/cloud/bigquery/storage/v1/JsonStreamWriterTest.java
index 258a287a1c..8c34ad9b3c 100644
--- a/google-cloud-bigquerystorage/src/test/java/com/google/cloud/bigquery/storage/v1/JsonStreamWriterTest.java
+++ b/google-cloud-bigquerystorage/src/test/java/com/google/cloud/bigquery/storage/v1/JsonStreamWriterTest.java
@@ -63,8 +63,8 @@
 @RunWith(JUnit4.class)
 public class JsonStreamWriterTest {
   private static final Logger LOG = Logger.getLogger(JsonStreamWriterTest.class.getName());
-  private static final String TEST_STREAM = "projects/p/datasets/d/tables/t/streams/s";
-  private static final String TEST_STREAM_2 = "projects/p/datasets/d2/tables/t2/streams/s2";
+  private static final String TEST_STREAM = "projects/p/datasets/d/tables/t/streams/_default";
+  private static final String TEST_STREAM_2 = "projects/p/datasets/d2/tables/t2/streams/_default";
   private static final String TEST_TABLE = "projects/p/datasets/d/tables/t";
   private static final ExecutorProvider SINGLE_THREAD_EXECUTOR =
       InstantiatingExecutorProvider.newBuilder().setExecutorThreadCount(1).build();
diff --git a/google-cloud-bigquerystorage/src/test/java/com/google/cloud/bigquery/storage/v1/StreamWriterTest.java b/google-cloud-bigquerystorage/src/test/java/com/google/cloud/bigquery/storage/v1/StreamWriterTest.java
index 134b438593..50e43fe45d 100644
--- a/google-cloud-bigquerystorage/src/test/java/com/google/cloud/bigquery/storage/v1/StreamWriterTest.java
+++ b/google-cloud-bigquerystorage/src/test/java/com/google/cloud/bigquery/storage/v1/StreamWriterTest.java
@@ -62,8 +62,10 @@
 @RunWith(JUnit4.class)
 public class StreamWriterTest {
   private static final Logger log = Logger.getLogger(StreamWriterTest.class.getName());
-  private static final String TEST_STREAM_1 = "projects/p/datasets/d1/tables/t1/streams/s1";
-  private static final String TEST_STREAM_2 = "projects/p/datasets/d2/tables/t2/streams/s2";
+  private static final String TEST_STREAM_1 = "projects/p/datasets/d1/tables/t1/streams/_default";
+  private static final String TEST_STREAM_2 = "projects/p/datasets/d2/tables/t2/streams/_default";
+  private static final String TEST_STREAM_SHORTEN = "projects/p/datasets/d2/tables/t2/_default";
+  private static final String EXPLICIT_STEAM = "projects/p/datasets/d1/tables/t1/streams/s1";
   private static final String TEST_TRACE_ID = "DATAFLOW:job_id";
   private FakeScheduledExecutorService fakeExecutor;
   private FakeBigQueryWrite testBigQueryWrite;
@@ -366,6 +368,31 @@ public void run() throws Throwable {
         });
   }
 
+  @Test
+  public void testEnableConnectionPoolOnExplicitStream() throws Exception {
+    IllegalArgumentException ex =
+        assertThrows(
+            IllegalArgumentException.class,
+            new ThrowingRunnable() {
+              @Override
+              public void run() throws Throwable {
+                StreamWriter.newBuilder(EXPLICIT_STEAM, client)
+                    .setEnableConnectionPool(true)
+                    .build();
+              }
+            });
+    assertTrue(ex.getMessage().contains("Trying to enable connection pool in non-default stream."));
+  }
+
+  @Test
+  public void testShortenStreamNameAllowed() throws Exception {
+    // no exception is thrown.
+    StreamWriter.newBuilder(TEST_STREAM_SHORTEN, client)
+        .setEnableConnectionPool(true)
+        .setLocation("us")
+        .build();
+  }
+
   @Test
   public void testAppendSuccessAndConnectionError() throws Exception {
     StreamWriter writer = getTestStreamWriter();