The giant Gulf of Mexico oil spill is breaching some of the apparently threadbare defenses that are being used contain it.

The National Wildlife Federation took a group of journalists on Thursday on a tour of some of the affected south Louisiana wetlands. Scientists on the tour took samples of oil that have washed into wild cane fields that tower more than 10 feet above the water.

The smell of oil hung tickly in the humid air and its presence was clear at the base of the green cane and reeds, which was darkly discolored.

Many of these small islands of wetlands were surrounded by the white protective boom which has been laid out to prevent the oil from seeping in. Clearly, the oil was flowing beneath it and/or washing over it, a point underscored by the dark splotching on the boom itself.

It is a well-established fact that this is  not 100 percent affective. The boom in this case, I was told, is absorbent boom, which is designed to repel water and soak up oil.

But with more oil expected to come in from the Gulf, the boom effort seemed almost futile.

Photo credit: Reuters/Lee Celano (Oil boom in Barataria Bay, Louisiana)