CAIRO: Swarms of jellyfish have descended on Egypt’s northern coast, keeping vacationers out of the water and stirring debate over a recent expansion of the Suez Canal.

The nomad jellyfish, Rhopilema nomadica, is native to the Indian Ocean and the Red Sea but has been turning up in the Mediterranean in growing numbers in recent years.

This year was the worst in recent memory. Wary bathers largely avoided the sea during the long Eid al-Fitr holiday last month, and social media was awash with pictures of the purple swarms and advice on how to treat stings.

The jellyfish have come through the Suez Canal, which was first built in 1869. It has been expanded on a number of occasions, most recently in 2015, through a multi-billion-dollar project that the government touted as an historic achievement.

Egyptian officials deny the recent expansion is to blame, noting that the jellyfish turned up in the Mediterranean as early as the 1970s.

“It is not the first time it appears on Egypt’s north coast. This time the number was just larger than previous years,” said Mostafa Fouda, an adviser to the Environment Minister.

The ministry said it has set up an investigative committee to look into the “unprecedented phenomenon.” But it said the invasion was likely caused by an abundance of food, an increase in organic pollutants and a decline in natural predators. It said global warming might also be a factor.

Experts interviewed this week said it was too soon to speculate on the impact of the latest Suez Canal expansion, but that a wider waterway would allow more jellyfish, and the organic matter they feed on, to flow from the Red Sea to the Mediterranean.

“The primary cause of the invasion of jellyfish is the Suez Canal,” said Jason Hall-Spencer, a marine biologist at Britain’s Plymouth University. “Other ecosystem stressors have allowed them to thrive and become a plague.”

Bella Galil, a scientist with the Steinhardt Museum of Natural History in Tel Aviv, also blamed the canal. She said pollution and global warming occur in much of the Mediterranean, but that only the Levant Basin — off the shores of Egypt, Israel and Lebanon — has five species of alien jellyfish.