"He apparently lost control. He hit a curb, which caused his vehicle to roll into a tree," Colarulo said.
Pratt, who wasn't wearing a seatbelt, was thrown from the SUV.
Police are still investigating the cause of the accident, but Colarulo said they don't believe alcohol or drugs were involved.
The Delaware County medical examiner said he died of "multiple blunt force injuries."
Episcopal coach Molly Konopka said the team decided after chapel services to row on Friday. But the freshman and junior varsity teams withdrew.
Five varsity teams decided to row Friday, including the varsity four, which was Paul Pratt's boat. Another rower, whom the coach declined to identify, will take Pratt's seat in the boat.
"They felt Paul would have wanted them to row," Konopka said. "That the way Paul was. Paul loved rowing. Paul loved competing."
Episcopal Academy is small private school in Newtown Square. It takes students from preschool through 12th grade, and the senior class has only 127 students, according to the website. Upper and middle school students attend chapel every other day.
The academy and some parents arranged for permission and buses to allow the entire junior class attend the regatta in Pratt's honor.
Classmates and friends have been posting remembrances on Twitter, using the hashtag #2014strong.
Jackson Collins, dean of the academy's Class of 2014, said Pratt "knew what he wanted and would do whatever was necessary in order to achieve it. ... Every week, you would see improvement."
Contact Jessica Parks at 610-313-8117, email@example.com or follow on Twitter @JS_Parks.