This year’s low-oxygen “dead zone” in the Gulf of Mexico is one of the largest ever, about the size of Massachusetts, and overlaps areas hit by oil from BP’s broken Macondo well, Louisiana scientists report.

The area of hypoxia, or low levels of oxygen, covered 7,722 square miles (20,000 square kilometers) of the bottom of the Gulf and extended far into Texas waters, researchers from the Louisiana Universities Marine Consortium said in a statement late on Sunday.

“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, the consortium’s executive director. “The total area probably would have been the largest if we had had enough time to completely map the western part (of the Gulf).”