It seems this year’s dead zone in the Gulf of Mexico, just off Texas and Louisiana, isn’t quite as big as was previously feared – however, it is still the third-largest ever mapped.

According to scientists, they are seeing crabs, eels and creatures swimming in crowds on the surface.. This is due to too little oxygen in their natural habitats at the bottom of the sea.

The ‘dead zone’ area is around 7,900 square miles and is in a state of hypoxia, meaning there is little or no oxygen in the zone. The size of the area is about the same as Connecticut and Delaware together and is the world’s second-largest hypoxic area. This year’s occurrence is around 7.5% smaller than was previously predicted judging by nitrogen levels in the Mississippi River watershed. Partly this is due to more storms than normal which kept the waters roiled and therefore reduced some hypoxia.

Hypoxia occurs when fresh water from the Mississippi River floats above the Gulf’s heavier salt water. Algae then die and fall to the bottom. Their decay uses oxygen faster than can be brought down from the surface. As the oxygen levels drop, the lower levels start to hold too little oxygen for fish and aquatic life to live, so they rise to higher levels. Nitrogen, which can occur thanks to fertilizer, erosion and sewage, speeds up the process by feeding algae. Scientists are trying to reduce the hypoxia in the Gulf, aiming for a hypoxic area covering just 2,500 square miles.

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