Premise: The ecological problems stem in large part from the fact that the brackish water and productive coastal wetlands and natural areas are often supplied with nutrient-rich irrigation return water, sometimes from rice farming. The Ebro Delta and its wetlands suffer similar water quality problems since they lie around the fringes of the large Delta farm region.
Hypothesis: The coastal wetlands are facing issues with ecology, which makes them seem to be non-productive due to the bad water.