Maine wardens returned Friday to Thompson Lake to look for witnesses who might have information about a boat crash Thursday that injured eight people, including five children.

Lt. Adam Gormely of the Maine Warden Service said investigators have seized both boats, one of which may not have been registered, and have interviewed the operators of each.

Gormely said wardens are still gathering more information to determine how and why the vessels collided.

“Right now we have a pile of information but we haven’t put it all together,” he said.

Of the eight who were injured, only two, both juvenile boys, remained in the hospital Friday. They were in stable condition.

The crash occurred shortly after noon Thursday on the Otisfield side of the lake in southern Oxford County. A 17-foot water-ski boat driven by Matthew Nolan, 58, of Potomac, Maryland, collided with a 19-foot open-bow boat driven by Ken Bartow, 60, of Biddeford, not far from the shoreline.

Bartow, his grandson and his grandson’s friend were thrown into the water. The unmanned boat then spun around and headed back toward shore before running aground.

Those boys, ages 9 and 10, are the two who remained hospitalized Friday.

A passenger in Nolan’s boat, which was pulling a water-skier, also ended up in the water.

The investigation will likely take several days. Gormely said he doesn’t believe alcohol was a factor but, as with all serious accidents, that will be part of the investigation.

Sharon Matthews, clerk for the town of Otisfield, said Bartow owns a camp on the lake and Nolan’s family does as well.

She said Bartow’s boat was registered with the town for 2015 but the registration for Nolan’s boat expired Dec. 31 and had not been renewed. Gormely said he thought both boats were registered.

The Maine Department of Inland Fisheries and Wildlife, which includes the Warden Service, maintains boat registrations and records, although many municipal tax collectors or town clerks are also recreational vehicle agents for the department.

Asked whether either boat operator had been involved in prior boating accidents, Gormely said he didn’t know but that it would be part of the investigation.

Bartow did not return a phone message left Friday.

Even though Maine’s many lakes and its coastline are popular in the summer months, boat accidents are relatively rare, Gormely said.

According to the U.S. Coast Guard, which compiles recreational boating data for all states, Maine averaged between 34 and 54 accidents per year between 2010 and 2014. That includes accidents on lakes and rivers as well as in coastal waters.

In 2014, 35 states reported more boat accidents than Maine, including nearby New Hampshire, which had 44, and Florida, which led all states with 581 boating accidents. Maine had 35 accidents that year.

Over the five-year period from 2010 to 2014, 31 boat accidents in Maine resulted in fatalities – 11 of them in 2011.

Data for 2015 so far were not available.

Gormely said quick thinking by witnesses, as well as life jackets, likely mitigated the impact of Thursday’s accident, which he said was among the most serious he has seen.

Harold Kowal, a retiree who lives on the lake with his wife, saw the crash and took his boat out to retrieve those who were thrown into the water. A visitor renting a cabin next door who is a paramedic also went out to assist Kowal.