For nearly a week, one of the world’s key shipping canals was blocked by one of the largest ships at sea, with billions of dollars in trade, from crude oil to live animals, delayed amid frantic efforts to refloat it.

The vessel — the 200,000-ton Japanese-owned Ever Given cargo ship — was freed Monday morning after a complicated rescue mission that drew attention from around the world as authorities and workers scrambled to unclog the crucial waterway. Since being refloated, the ship has been anchored midway through the canal, in the Great Bitter Lake.

On Wednesday, Egypt launched an investigation into the incident, Sayed Sheaysha, a Suez Canal Authority adviser, told the BBC. Experts boarded the ship to collect information about the crew’s actions and preparedness.

With about 400 ships backlogged as of Monday, Egyptian authorities doubled the number of ships cleared to pass through the canal a day, the Wall Street Journal reported, potentially putting further pressure on the crews of vessels and pilots assigned to guide them.

Here’s what happened.

What is the Suez Canal, and who controls it?

The 120-mile-long Suez Canal is a man-made waterway linking the Red and Mediterranean seas. It is owned by Egypt.

When it opened in 1869, the canal increased the ease of global trade by offering a route that circumvented the Cape of Good Hope in Africa. It remains crucial to international trade, including for the oil sector.

In 1956, Israel, Britain and France invaded Egypt in an attempt to seize control of the strategic waterway after the country nationalized it. Their forces later withdrew after the United States withheld support.

Egypt launched a major and costly renovation of the canal in 2015.

How did the vessel get stuck?

Now that the ship has been freed, focus will shift to figuring out the answer to that question.

Here’s what we know: During a sandstorm March 23, the Ever Given cargo ship, operated by Taiwanese company Evergreen Marine, was battered by heavy winds. Some experts theorize that the large number of containers it was handling may have acted as a sail and pushed it off course.

But other factors could have been involved. Lt. Gen. Osama Rabie, head of the Suez Canal Authority, said authorities haven’t ruled out the possibility of “a technical error or a human error.”

Cargo-ship navigation through the canal is a carefully planned operation. More than 50 ships passed through it on average each day last year, according to figures from the Suez Canal Authority.

Rabies said Monday that the two pilots who assisted the Ever Given were “extremely experienced” and noted that the boat’s captain was ultimately responsible for the safety of the ship. While canal pilots do not steer the ship, they’re supposed to offer guidance to captains based on their local knowledge and expertise, and help vessels make a safe passage.

The incident is also likely to raise questions about whether container ships have gotten too large — and whether the Suez Canal can safely handle them.

Although the expansion completed in 2015 provided two shipping lanes for some parts of the canal, the area near the Gulf of Suez where the Ever Given got stuck on Tuesday is in just one 984-foot-wide lane.

The Ever Given is one of the largest ships in operation, at 193 feet wide and 1,312 feet long, exactly the maximum length allowed in the canal. Larger than the Eiffel Tower, the ship would take up much of the space in Washington’s Tidal Basin.

What was done to get it out?

Teams were brought in from around the world to try to figure out how to move the ship. For days, dredgers removed literal tons of sand and silt from around the ship’s hull, while tugboats attempted to pull the vessel away from the canal banks.

Their efforts were aided by a king tide late Sunday night — an unusually high tide that occurs in spring when the moon is full. The rising waters helped to lift the boat, and after frantic efforts overnight, the Ever Given was largely freed by Monday morning.

Ragui Assaad, a professor at the University of Minnesota who focuses on the Egyptian economy, said it was not a simple task.

“I think part of the issue is that the canal is not that wide and so the ship actually hits both edges when it goes sideways,” Assaad said, adding that the sides and base of the canal were “soft sand” that allowed the ship to sink into them.

If tugboats and dredgers hadn’t succeeded at dislodging the boat, the next step would have been to begin removing the tens of thousands of containers on board. Doing so would have required specialized helicopters and extra-tall cranes, and been an extremely time-consuming process. Some experts cautioned that removing the load could also run the risk of damaging the boat or unbalancing it, further wedging it into the sand.

How has the stranding affected international trade?

About 13 percent of world trade passes through the Suez Canal, according to Allianz, an investment firm. Even a return to normal operations in a week or so would leave supply chains struggling to work through the accumulated backlog.

“So the knock-on impact is not going to be measured in days or weeks,” said Douglas Kent, executive vice president of strategy and alliances at the Association for Supply Chain Management. “It’s going to be measured in months.”

Oil prices shot up and down after the ship became stranded.

Lloyd’s List, a shipping journal, estimated each day the canal was closed, some $9 billion worth of goods were affected, the Associated Press reported. Delays at the canal will affect unloading schedules at other ports and docks, which can delay goods en route to producers, suppliers and consumers.

“Once you open the canal, it’s like ketchup out of a ketchup bottle,” Lars Jensen, the chief executive of Denmark-based SeaIntelligence Consulting, told The Washington Post.

Ships that opted to take an alternative route around Africa and the Cape of Good Hope faced lengthy delays, adding as many as 15 days to their journey.

What could change moving forward?

Egypt’s investigation into the matter, if human or technical errors are found, could change practices in the canal.

Broadly speaking, the shipping industry could see a reckoning with some of the risks posed by the canal as a chokepoint.

Egyptian President Abdel Fatah al-Sissi said the event had demonstrated the “reality and importance” of the canal. But the scale of the incident could lead to reconsideration of route and ship size. “We kind of underestimated the risk of going through the Suez Canal,” Genevieve Giuliano, a professor at the University of Southern California’s Sol Price School of Public Policy who has served as an adviser to the U.S. Transportation Department on freight logistics, told The Post, saying that the industry could also eventually shift away from the very large ships that ports have gone to great lengths to accommodate.

The stranding also put a spotlight on the plight of workers in the shipping industry during the coronavirus pandemic, hundreds of thousands of whom have been essentially stranded aboard vessels amid border restrictions.

Ruby Mellen, Jennifer Hassan, Antonia Noori Farzan, Sudarsan Raghavan, Ishaan Tharoor, Brian Murphy and David Lynch contributed to this report. Additional graphics by Tim Meko and Hannah Dormido.