GRAND ISLE, La.—Twelve-foot high waves have hampered the collection of oily water by the Taiwanese ship A Whale, which continued testing its prowess on Monday as the world's largest skimmer.

The effort is the latest in a series of urgent and desperate attempts to stanch the flow of crude flowing onto the fragile Gulf of Mexico coast, home to many varieties of waterfowl and sea life. The flow stems from the April 20 explosion of the Deepwater Horizon drilling rig leased by BP PLC.

On...