The annual summertime dead zone caused by low oxygen levels in water along the Gulf of Mexico shoreline this year is twice as big as last year’s, stretching 7,722 square miles across Louisiana’s coast well into Texan waters, scientists with the Louisiana Universities Marine Consortium announced Monday.

But there’s no evidence the larger expanse of low-oxygen water — which covers an area as big as Massachusetts, and is linked to nutrients carried to the Gulf by the Mississippi River — was made bigger by the Deepwater Horizon oil spill, scientists said.

Last year, the area affected by low oxygen was limited by lower springtime water levels in the Mississippi River, which meant less nutrients reached coastal waters. Also, persistent winds from the west and southwest last year may have driven low-oxygen water out of the easternmost Louisiana waters where last year’s mapping was done.

The size of this year’s dead zone might actually be larger than mapped. LUMCON’s RS Pelican research ship found a large area of hypoxia, or low-oxygen water, along the coast west of Galveston Bay and offshore in that area, but was unable to finish mapping there before returning to map an area east of the Atchafalaya River.

“This is the largest such area off the upper Texas coast that we have found since we began this work in 1985,” said Nancy Rabalais, executive director of LUMCON and chief scientist for the dead-zone cruise.