Why was the Union naval blockade of Confederate ports called the “Paper Blockade”?

Scott's Great Snake

The Union Blockade, nicknamed Scott's Great Snake, made the open harbors of California desirable to the Confederacy.

During the First World War, Britain intended to use its powerful navy to starve Germany and Austria-Hungary into submission. By maintaining a blockade of enemy ports it hoped to cut off supplies from the outside world.

answer; i believe the correct answer is (the willamete valley);