In recent years there has been a growing concern about a large area of oxygen-depleted waters that develops seasonally in the Gulf of Mexico near the mouth of the Mississippi River. The size of the oxygen-depleted area varies from year-to-year and has extended from the mouth of the Mississippi River west to near the Texas border. Oxygen depletion in the nearshore Gulf can exceed 6,000 square miles in size and may form as early as February and last as late as October with the most widespread and persistent conditions occurring from Mid-May to Mid-September.