Who won the Second Battle of Ypres?

In a sense no one won the battle. The stalemate on the Western Front was not broken by the German offensive or the Allied counter-offensive.

However, if a winner is to be given, it would be the Alllies. The British and Canadian troops at Ypres successfully held the line against poison gas and a massive German offensive. But the cost was horrific with 70,000 Allied dead, wounded, or missing and 35,000 German dead, wounded, or missing between April 22 to May 13, 1915.