Rick Outzen documents in his blog how fishermen were instructed to ignore large tar balls and the Coast Guard's use of dispersants. It's valuable information, and I know it's true because I talked at length with a boat captain in the Vessels of Opportunity program who was sent out with a BP team to collect water samples. They collected some where he could clearly see a lot of oil--and then BP threw out those samples because they had been "collected improperly." But he observed the whole process, and knew they were collected in exactly the right way.
Read Rick Outzen's blog post here.